Mysterious Building

When I turned several narrow streets to find this small building hidden in the surrounding steel jungle, I couldn't believe that there was such an old building in such a prosperous area. It was incompatible with the surrounding buildings, as if it appeared out of nowhere. The peeling outer wall was an ugly mixture of black and green. A continuous patch of dark green moss grew on the wall of the first floor, and it had a tendency to climb upward. The rusty iron door in the middle of the small building, which was the only entrance and exit, was ajar, leaving only an empty hole where the keyhole should have been...