A spectacular underwater tunnel carved through the rocky coastline of Proti Island creates one of the most unique and photogenic dives in Messinia.

Dive Overview

The steep and rugged coastline of Proti Island may appear hostile from the surface, but beneath the waves it hides dramatic underwater formations ideal for exploration.

One of the most famous features of the island is the “Blue Hole,” an underwater tunnel cutting through a rocky headland on the island’s western side facing the Ionian Sea.

The dive combines a swim-through cavern experience with steep underwater walls, crystal-clear blue water, and the raw atmosphere of the open Ionian coastline.

Entry & Conditions

The dive site is accessible only by boat.

The closest harbor is the small port of Marathos (Marathopoli), approximately 2–3 km away.

Because the site faces the open Ionian Sea, conditions can change quickly depending on wind and swell. Morning dives are strongly recommended, as weather and wave activity often increase later in the day.

A useful local rule is that the sea conditions at the entrance of Marathos harbor usually reflect the conditions at the Blue Hole itself.

The boat can anchor inside the small cove formed by the steep cliffs near the dive site.

Entry is performed directly from the boat using either giant stride or back roll entries.

What You’ll See

The Blue Hole tunnel lies on the northern side of the cove at approximately 7–7.5 meters depth, making it accessible to divers of all certification levels.

After a short surface swim, the entrance of the tunnel becomes visible, illuminated by the blue Ionian light passing through from the opposite side.

Divers enter the tunnel one at a time. The passage is approximately 20 meters long and wide enough for comfortable transit without touching the walls.

Depending on sea conditions, mild to moderate surge or current may be present inside the tunnel.

Exiting the Blue Hole reveals dramatic underwater walls descending toward deeper sandy bottoms beyond 30 meters.

Divers can continue westward exploring the vertical rocky formations and deeper sections according to their certification level, air supply, and comfort.

The return dive is usually completed by passing once again through the Blue Hole and returning to the sheltered cove for the safety stop.

Important Consideration

• Boat access only
• Open exposure to Ionian weather and swell
• Surge and current possible inside the tunnel
• Maintain good buoyancy inside the swim-through
• Morning dives recommended for calmer conditions

Depth Profile

The Blue Hole entrance begins at approximately 7 meters depth, while the surrounding walls descend beyond 30 meters.

Tips for Divers

• Bring a torch to enhance colors inside the tunnel
• Enter the swim-through one diver at a time
• Avoid touching the walls or ceiling
• Watch for surge if the surface is rough
• Excellent site for wide-angle photography

Why This Dive Stands Out

The combination of a natural underwater tunnel, dramatic Ionian cliffs, and crystal-clear blue water makes the Blue Hole one of the most atmospheric and memorable dives in western Greece.