You step down into the cold salty sea and walk down the steps. When you reach the bottom of the stairs and move around the corner, you are all easily waist deep in the water and you can feel that the ground has turned to sand and small stones.
You move along the side of the structure facing the ocean and on your right stands a dark doorway, dominated by an ajar rusty metallic grate door. It clearly leads into the structure. You can hear the sloshing of the deep water inside and you can see the gargoyles from the roof peering down ominously at you, their stony forms silhouetted against the dark sky and flashes of lightning.
Without light, the inside of the structure is pitch black. Hrimr's darkvision allows him to see and communicate that the doorway leads to some kind of an old loading dock area and a long hallway that leads deeper into darkness. The water appears to remain at a constant height inside.