Agios Sostis: Marathonissi, Keri Caves, and Turtle Spotting

The best reason to book this three-hour trip is the chance to see Caretta Caretta loggerhead turtles in the protected waters around Zakynthos. The glass-bottom boat adds a useful view below the surface, while the route brings you close to the Keri Caves and Marathonisi.

I like the roomy boat, with shaded seats and a rear sundeck, and I like the good mix of swimming, scenery, and beach time for $29. The main consideration is that turtle sightings are never guaranteed, and several boats can gather around one animal.

Key points

• Glass-bottom views: Look beneath the boat for a glimpse of the marine life and clear water around Zakynthos.
• Keri Caves swim stop: Swim in the Keri Caves area and Oasi Bay, where limestone walls meet striking blue water.
• Marathonisi beach time: Spend about an hour on the island, but only a small section of beach is open because it is a turtle nesting site.
• Three-hour format: This is a compact outing that fits neatly into a morning or afternoon in Laganas.
• Friendly multilingual hosting: The captain speaks Greek and English, and several bookings praise the crew’s humor, care, and flexibility.
• Bring your own kit: Pack sunscreen, a hat, swimwear, towel, snacks, drinks, and snorkeling gear. Large bags are not allowed.

A Short Boat Trip With Three Strong Draws

This excursion works because it does not ask you to choose between swimming, wildlife, and scenery. In three hours, you get all three, with the glass-bottom boat providing an extra look at the water as you move through the National Marine Park of Zakynthos.

The route begins at Agios Sostis harbor in Laganas. Look for the Nautilos flag positioned directly in front of the boat. The captain welcomes you there, so arrive knowing that this is a harbor meeting point, not a hotel pickup service.

I see this as a relaxed introduction to the southern coast of Zakynthos. It is not a full-day sailing adventure, and it does not promise long periods on empty beaches. Instead, you get a focused outing with a clear purpose: see the marine park, try to spot turtles, swim in a boat-access-only area, and spend time on Marathonisi.

Why the Glass-Bottom Boat Matters

The glass panels are not a substitute for snorkeling, but they make the ride more interesting. As the boat moves over clear water, you can look down and get a sense of the underwater world without being in the sea.

That matters if you are traveling with children, do not want to snorkel, or simply enjoy watching the water while the boat is underway. The boat also has a shaded seating area, which gives you a break from the sun, plus a rear sundeck if you want more open air.

I would choose a seat with shade at the start, especially in summer. You can move around later, but having cover is useful during the ride and while waiting for a turtle sighting.

The boat is described as roomy, and one booking specifically praised the space available. That is a small detail, but it can make a real difference when you are sharing the boat with other groups and carrying swim equipment.

The Keri Caves Area and Oasi Bay Swim

The first major stop is in the Keri Caves area, including Oasi Bay. These locations are accessible by boat, and the appeal is immediate: clear water, pale limestone, and sheltered coastal scenery that you cannot reach from the road.

You have the chance to swim in the area and take photographs from the boat. The water near the caves is especially attractive when sunlight reflects off the limestone walls. The blue color changes as you move between open water and the rocky edges.

One important correction to keep in mind: you do not swim inside the cave itself. The stop is near the cave area, where you can enter the sea and enjoy the setting from the water. This distinction matters if you are booking because you expect a cave-swimming expedition.

The swim stop is one of the strongest parts of the trip. It gives you time to cool off rather than simply pointing out the caves from a distance. Pack a towel and swimwear, and bring snorkeling gear if you already have it. Snorkeling equipment is recommended in the preparation notes, but it is not listed as supplied.

Use care around the rocks. One person cut a foot after slipping, and although the captain helped, the incident is a reminder to move slowly when entering or leaving the water. Water shoes may be useful, but they are not specifically listed as required equipment.

Turtle Spotting in the National Marine Park

The trip then turns toward one of Zakynthos’s best-known wildlife experiences: looking for loggerhead turtles in their natural habitat. Marathonisi and the surrounding waters are linked with the turtles, and the island serves as a breeding ground for them.

The glass-bottom boat helps you watch the surface and the water below. The captain’s experience also matters here. Several bookings praised captains who knew where to look, explained the surroundings, and kept the mood light. In one autumn outing, the captain pointed out a Caretta turtle and shared stories about the island.

Still, you should treat turtle spotting as a possibility, not a promise. Wildlife follows its own schedule. One July trip happened after some turtles had already left the area because their eggs were hatching, yet the group still saw several turtles.

This is also the part of the excursion where responsible behavior matters most. One account described several boats gathering around a single turtle and felt that chasing the animal was wrong. If your boat finds a turtle, I would watch quietly, keep a respectful distance, and avoid treating the animal like a moving photo target.

That concern does not cancel out the value of the experience. Seeing a loggerhead in protected waters can be memorable, especially for children. It simply means the best trip is not the one that gets closest. It is the one that lets you observe without adding pressure to an already protected species.

Marathonisi, Also Called Turtle Island

Marathonisi is the second major stop. As you approach, you can see the island’s pine, olive, and green oak vegetation, along with its small beach. The island is often called Turtle Island because of its connection with the loggerhead turtles.

You get free time to explore the accessible part of the island, swim, or sit in the shade. A bar sells snacks, drinks, and ice cream, but those purchases are not included in the $29 price.

The beach stop is useful, but keep your expectations measured. Only a small section of the beach is open because the shore is protected as a turtle breeding ground. You are not getting an unrestricted island beach day, and the accessible beach may feel ordinary compared with the dramatic cave scenery.

One booking described Marathonisi as a mediocre beach and suggested the tour might improve with another stop. I think that is fair criticism for anyone mainly interested in beautiful beaches. The island’s value lies more in its protected status, turtle connection, and position within the marine park than in beach quality alone.

You may also find the one-hour break longer than expected if you were not told about it clearly. Use the time for a swim, a snack, or a quiet look around, but do not expect a long island walk. The protected beach area limits what you can do.

What You Get for $29

At $29 per person, this is a strong-value outing if you want several experiences in one short trip. The ticket includes the glass-bottom boat, a visit to Marathonisi, a swim stop, views of the Keri Caves, and swimming near Oasi Bay.

That price does not include hotel pickup, food, drinks, or ice cream. You need to reach Agios Sostis harbor yourself and budget separately for anything purchased on Marathonisi.

The value is strongest for people staying in or near Laganas who want an affordable boat trip without committing most of a day. You get a proper coastal outing, rather than a brief harbor cruise, and the route includes the area’s main natural attractions.

It is less compelling if you want a quiet private boat, a long snorkeling session, or a full day on an island beach. This is a shared excursion with several scheduled elements, so the time at each stop is limited.

The three-hour length is a practical advantage. You can book it around other plans, return to Laganas for lunch, and still have time for the rest of your day. The tradeoff is that the schedule may feel brisk, especially if you want to linger in the water.

Timing, Meeting Point, and What to Pack

The boat leaves from Agios Sostis harbor in Laganas. Find the Nautilos flag directly in front of the boat, where the captain will meet you. Hotel transport is not included, so plan your own way to the harbor.

Starting times vary, and you should check the available departure before booking. The operator offers free cancellation up to 24 hours in advance and a reserve-now, pay-later option, which can help if your Zakynthos plans are still shifting.

Bring:

• Sunglasses
• A sun hat
• Sunscreen
• Swimwear
• A towel
• Food and drinks
• Snorkeling gear

You can buy refreshments on Marathonisi, but bringing water and a snack gives you more control over the short schedule. Large bags and luggage are not allowed, so use a small day bag.

The boat has shaded seats, but do not treat that as full protection from the sun. You are spending time on open water and on a beach, so sunscreen and a hat are basic equipment, not extras.

The Captain Makes a Difference

The captain is the main human part of this experience. The host speaks Greek and English, and the strongest outings have included friendly, funny, accommodating captains who explain what you are seeing and help when plans shift.

A slight departure delay occurred on one trip, but the group was notified in advance and the captain tried to accommodate everyone. That suggests you should allow a little flexibility around the start, even though the advertised duration is three hours.

The tone seems informal rather than lecture-heavy. You get stories, directions, and practical help, not a long formal presentation about marine biology. That suits a short boat trip, especially if you want to swim and take pictures rather than sit through a talk.

For families, a good captain can make the difference between a simple boat ride and a memorable outing. Children have enjoyed the turtle sightings, the swim, and the glass-bottom view. Parents should still watch children carefully around the boat, the water, and the rocky edges of the swim area.

Who Should Book This Trip

I would recommend it to you if you want:

• A reasonably priced boat trip from Laganas
• A short outing instead of a full-day cruise
• A chance to see loggerhead turtles without booking a dedicated wildlife expedition
• Swimming in clear water near the Keri Caves area
• A family-friendly mix of wildlife, scenery, and free time
• A boat with shade as well as an outdoor sun deck

It suits couples, families, and first-time visitors who want to see several highlights of southern Zakynthos in one booking. The multilingual captain and relaxed pace also make it practical for an international group.

I would think twice if your priority is a secluded beach, a private experience, or guaranteed wildlife photography. The turtle sighting may be excellent, but it depends on nature and on how many boats are in the area. Marathonisi is protected and scenic, but the open beach area is small.

Is the Agios Sostis Boat Trip Worth Booking?

For $29, I think this is a sensible choice for most people staying around Laganas. The trip gives you the Keri Caves area, Oasi Bay, Marathonisi, a swim, and a real chance to see a loggerhead turtle, all within three hours.

Book it for the combination of experiences, not for a perfect beach day or a guaranteed close-up turtle photograph. Pack light, protect yourself from the sun, keep your distance from wildlife, and treat Marathonisi as a protected natural stop rather than a resort beach.

If those expectations fit, this is an easy, affordable way to get out on the water and see a more natural side of Zakynthos.

FAQ

Where does the boat tour meet?

The meeting point is Agios Sostis harbor in Laganas. Look for the Nautilos flag directly in front of the boat, where the captain will welcome you.

How long does the excursion last?

The tour lasts three hours. Starting times vary, so check availability for the departure options on your chosen date.

Is hotel pickup included?

No. Hotel pickup and drop-off are not included, so you need to make your own way to Agios Sostis harbor.

Can I swim inside the Keri Caves?

No. Swimming inside the cave is not allowed. The tour includes a swim stop in the Keri Caves area and near Oasi Bay.

Are food and drinks included?

No. Food and drinks are not included. You can purchase snacks, drinks, and ice cream from the bar on Marathonisi, or bring your own supplies.

How much of Marathonisi beach can I visit?

Only a small portion of the beach is accessible because the beach is protected as a loggerhead turtle breeding ground.

What languages does the host speak?

The host or greeter speaks Greek and English.