Symi Maritime Museum Attraction
It is housed in a neoclassical house of Gialos since 1990 and it hosts nautical equipment, parts, tools and ship models of local ships. One section of it is devoted to the sponge diving, which has a long tradition on the island, with diving machines, diving gear and sponge species. You will find it right behind Kampos, the main square.
This place has been closed for the past few years and may be closed for good.
Save yourself the trouble and please call/ask before heading there.