Marathonisi and the Keri Caves

Marathonisi is the small, low, turtle-shaped islet in Laganas Bay that gives the cruise its nickname of Turtle Island. The bay is the most important nesting area for the loggerhead sea turtle, known as Caretta caretta, in the Mediterranean, and the boats that leave Laganas, Kalamaki and Keri spend the first part of the trip slowly cruising the protected waters where turtles surface to breathe. Skippers know where to look, and the usual routine is to idle the engine, scan the water and point out a head or a shell to passengers, who often cheer when one appears. Sightings are never guaranteed, and the best operators say so, but a quiet boat in calm water gives a good chance of seeing at least one. From the bay, the boat runs along the southwest coast of the Keri peninsula to a line of sea caves and rock arches, where the cliffs are streaked with ochre and green and the water turns glassy and clear. Passengers swim in shallow, protected coves, and some trips stop at the sandy shallows of Marathonisi itself, where landing is allowed only in the permitted zones.

The experience depends on the rules that protect the turtles. Laganas Bay is part of the National Marine Park of Zakynthos, and boats must keep to marked speed limits and distances, avoid the nesting beaches and never feed or touch the animals. Responsible operators follow these rules strictly, and you should favour them: ask whether the boat uses a glass bottom or clear hull, whether engines are cut when turtles are close, and whether the operator keeps to the park guidelines.

Disturbing turtles is not only illegal but also reduces the chance of seeing them, because they dive when boats approach at speed.

Choose the type of trip to suit the group. A glass-bottom boat lets children watch fish and seabed through the floor, and it is easy for older travellers because the deck is stable and the swim stop is optional. A smaller boat is more flexible and can reach the narrow cave entrances, while a private charter allows a slower, longer route. The cruise usually takes between three and four hours and runs in the morning and the late afternoon, and the morning departures tend to have calmer water and clearer views into the bay.

The Keri caves are worth the second half of the trip. The headland is formed of pale limestone that the sea has hollowed into pockets and tunnels, and the water inside them shows every shade from pale aqua to deep blue. Some boats stop at the pair of rocks known as Mizithres, which are the most photographed formation on this coast. Sunscreen should be reef-safe, and visitors should bring a hat, water and a towel, since shade on deck varies by boat.

For first-time visitors, this is the best-value water day on the island: it fits into a morning, it is relatively cheap, and it suits families as well as couples. The paid product below is a shared cruise that covers Marathonisi, the Keri caves and the turtle-spotting stretch in a single trip. Book a few days ahead in summer, and be ready to have the plan changed if wind makes the Keri coast rough.