I've done the Rotherhithe Tunnel a few times, and it's no fun, but a looooong time ago I did the Blackwall Tunnel, and it was fantastic. As in really stupid, but fantastic. And don't.
I've asked about the Limehouse Link, but, sadly, the owners say that they would shut it, and send you a bill for the expense incurred, which would, by the time m'learned friends added their little bit, be a fortune. And I've always wanted to do the Strand underpass, but haven't worked up the courage.
Some thirty years ago I went on a pass busting mission to the Pyrennees with my brother. We were so anxious to save weight that we took one front light and one rear light between us. And so we found ourselves in a completely unlit and unlined tunnel on what is now the N-260. And we couldn't see squit. Only a little hole of light a long way off to steer by. And halfway down, my brother, who was in front, braked and said...'this is silly'. I was in no position to disagree, as I'd just run in to the back of him. A truck appeared at the end of the tunnel behind us, with a roar that shook our bones. We shot out of that hole in the ground like champagne corks...