London, England is good for that. Several years ago they found an entire wooden sailing ship in an enclosed drydock off the Thames, in a building which the government was paying to keep maintained and guarded, but which no-one had entered in centuries.

I think it was also in London that during demolition of a parking garage a few years ago they found an isolated nook with a car which had been there for decades. (IIRC the owner had reported it stolen when he couldn't find it.)