There is a handy tunnel that connects the main three museums in London. It starts at South Kensington Underground and goes to the Natural History Museum, the Victoria and Albert and the Science Museum. I have found it very useful on the occasions where the rain is pouring down outside and you a) Need somewhere to hide, or b) want to take a very slow walk to the next museum.
The tunnel must have perfect acoustics as it is always full of buskers, most are great but some think the acoustic properties naturally make their singing better. It does not.