Well there it is... I was looking for that library. 

C'mon, the guy's been locked up for hundreds of years with only a dragon and a bunch of slavering demons for company. The only way to stay sane is a decent library! 

Oddly enough the lost library shouldn't be able to spawn on rivers (at all)... that is in the code. The blocked arctic river terrain blocks used to contain ice mountains to show the fact that it was impassable. You seem to have problems with these lost libraries.

You could always give him a helpful poke....with the pointy end of your weapon!

re that first pic

I think a lost library in a similar spot caused every single enemy sovereign to park an army in the master quest area one recent game.  I had opened the first gate, but when I returned it was packed 4 deep.  It turned out to be easier to go for the domination win while they were all stuck.  Small map, probably all the other loots were already collected.