There's an island near the coast of Taiwan where one of my fellow exchange students lived with his host family. That island (Kinmen) is populated, but pretty sparsely.
As you may be aware of, Taiwan and China aren't on the best of terms, and since Kinmen is located between Taiwan and mainland China, it has become a bit of a military base. Though a lot of those military installments are active and not accessible for tourists, one particular building has been abandoned. This building - part look-out towers, part underground - can be reached by foot only when the tide is low, otherwise the path leading towards it gets flooded. My friend and I decided to explore a bit, and though nothing was locked or otherwise forbidden to enter, it did feel very eery and like we shouldn't really be there. At the time, we were the only people there, though it was obvious that the place is frequently visited - probably by other tourists, wanting to have their own little adventure.
The next story happened on the same island, though with a vastly different context. As I said, Kinmen is populated, but most inhabitants live in a cluster of modern buildings, while a part of their historical village is being used as a tourist attraction. Once you move past the polished plaster and brightly coloured curtains, it's a different view though: Narrow alleys, uneven pavements, dusty red bricks. We wandered those empty streets for quite a while, and then came across a two storey building that looked like it had sprung from a Studio Ghibli movie: Half-collapsed stairs, window frames with missing glass, holes in the roof, but perhaps the most spectacular thing were the greenery sprouting from every nook and cranny, filling doorways and peeking out the windows, making the whole building look like an enchanted garden. I wish we could have gone inside, but every entrance was blocked with metal bars.
