Dark Souls - Skyrim vs Dark Souls

It's around the area where you fight the crystalisk 'Blue'. Once you've dealt with him, there'll be an island a distance off from the shore. If you're of high level and/or a gunzerker, you can be able to sprint all the way through the acid towards the island, switching on gunzerking when your health is low.

Just found the Dark Souls reference in Caustic Caverns.