No, is not a Hobbit film stage. Suomenlinna is an island in Helsinki, Finland that was used as a military base to protect the shores from Russian expansionism. Today is an Unesco World Heritage Site that attracts a lot of locals and tourists. It is actually a popular spot to have picnic during summer.
The composition is based on the remnants of the weapon warehouses that fed the still mounted 280mm... Russian cannons.
I want to go back and have a sandwich.