Describe an interesting old building you have seen

The building I want to describe is the central post office in Ho Chi Minh City, which was built at the end of the nineteenth century. From outside it looks like a European railway station — arched windows, a big clock, yellow walls — but the surprise is inside: one huge vaulted hall with two enormous hand-painted maps on the walls, drawn when the city looked completely different. What makes it interesting to me is that it still works as a real post office. Between the tourists taking photos there are people genuinely posting parcels, and there used to be a famous letter-writer who translated letters for customers at a little wooden desk. Most old buildings survive by becoming museums; this one survives by simply refusing to stop doing its job, and I find that far more impressive.