I visited Billingsgate Roman House and Baths as part of Open House London. There was a small queue to get in, as numbers down to the remains have to be restricted but it passed quickly and we were given an interesting talk about the remains while we waited. First discovered in 1848, outside of the arrangements for Open House London they can be visited at only certain times between April and November, so do check their website before making a visit.
Louise Jayne's Blog 