Foley Street Studios
As you travel around London, you will see quite a few structures similar to this, with staircase down. They used to be public toilets, but were sold off some years back, and became all sorts of enterprises. This on Foley Street was a film or tape studio for a while, they put the taller structure inside the old. My favourite example, though, was the one that turned into an upright tanning shop. Their slogan? Tanning at your conveniene.