I'm currently in London, by the way, and my only guide is a waterlogged copy of the 2000 edition of Frommer's Guide to England, which I found on the sidewalk in Park Slope a couple of months ago. (Or, more accurately, my only guide are the ten pages that I excised from the center of the guidebook before my departure, in order to save weight.) It's pretty accurate, I guess, but I still had to go online to verify that there was such a place as the Tate Modern.