The Tregastel Marine Aquarium nests in pink granite caves and presents Breton marine life living in three different zones defined by the height of the tide: the Sea-Spray Zone, the Tidal Zone and the Sub-littoral Zone. In turn, chapel, Second World War ammunition depot, habitation, the Marine Aquarium will surprise the visitor wandering among the impressive natural blocks of pink granite.

According to geologists, the pink granite was formed 300 million years ago. It slowly cooled in the sub-stratum, which would explain its coarse-grained structure (mica, grey quartz, feldspars).

In our region, the distinctive rounded lumps of granite are the result of fissures which cut the rock into parallelepipeds. Water infiltrated into these fissures and little by little altered the rock forming the granite arenas. At the end of several millions of years of erosion due to the effects of sea-spray, rain and the sea, the edges of the parallelepipeds became rounded.

The granite arenas disintegrated into sand, forming the sandy beaches and rounded granite rocks.

Situated above the high-tide water mark, this zone is extremely unfriendly to both fauna and flora. Only a few species have managed to adapt to these extreme conditions: the rain, wind and salt prevent any terrestrial plant from living here. It is the world of the lichens, organisms half-way between algae and fungi, the world of animals capable of moving around.
This open-air zone allows children and adults alike to get to know the first animals of the Aquarium in the outside tank. Maritime plants which grow along the seashore embellish the visit.