What is the object ?

by Kazu

Above is the broken concrete dome on the rock field. What was on these concrete bases?
If a special restaurant or beach cottage had been on them, it was so interesting.

 So many mussels and balanomorphas
could be seen through the salt water. When human beings see the ocean from above, they may feel kind of fear.

But once you dive into the ocean and see them from the same level, you will be so intrigued by the way they live, I think.