One of my favourite tiny blink-and-you'll-miss spots like this is a completely unassuming building in eastern Chania in Crete, which is a Venetian storefront/apartment, built on top of a Classical foundation, with Minoan ruins in the deep basement that are on display to the street via glass and interpretive signage, that used to host a video game store and I think now is a smoke shop. It's just a fascinating layering of multiple millennia of history