Mug House, London Bridge, SE1

Accessed via a small entrance beneath the railway bridge, it's a veritable warren inside, and much larger than you might expect as you navigate the different drinking areas. It's actually more comfortable than I expected. Unfortunately there's now no real ale, but there was some hoppy keg stuff that tasted OK. It's fine if you're alright with subterranean drinking with no natural light and don't suffer from claustrophobia.