not trying to be contrarian but a church inside a river loop sounds like a super sacred church that requires a pilgrimage to visit.

That said, there's an Apple TV video of a castle on an island where my first thought was "why does this exist?"

https://vimeo.com/657386068

> "why does this exist?"

"Though hidden from the sea, the castle controls access to Loch Shiel" says Wikipedia. Which is a sensible thing for a castle to do back in the olden times.

Plus it's a tidal island - you can just walk across. Don't even need a drawbridge (although I guess that makes defending attacks from inland a bit tricky.)

https://en.wikipedia.org/wiki/Castle_Tioram