A now-dry underground water cistern has been converted into a one-room museum of water technology demonstrating how desert cities like Qa'en traditionally managed to keep themselves green. Curiosities in the collection include a saucepan-like copper water clock, designed to time 22-minute intervals. Without a translator it's hard to learn much beyond admiring the photo panels, but it's arguably worth the modest entry fee just to descend the illuminated brick stairway.
Start from the brick-framed doorway, two doors towards the Jameh Mosque from 2nd Alley. If no one's there, get the key from the Anthropology Museum or call Ali Sarafiyan (0912 018 9580).