I had a look through these:
And decided to make a tower in the middle of the lake and even got quite far with it:
The idea is that there's some kind of a building in the middle of the lake and it's getting covered with vegetation and somebody's trying to repair it. However there's something I don't like about it and I can't quite come up with a good story for it.
So I came across these:
http://www.criteriondg.info/wordpress/uploads/scott-wills.jpg
and thought I could make a dome where the opening of the lake is. I was struggling to figure out how to make a believable rock mesh.
Devil's causeway in Ireland has these six angled basalt towers. Because they sit next to one another perfectly if I can just make one and and make a nice composition of its uv mapped duplications. I get away with minimum uv mapping and the whole scene will be easy to manage.