Did you know that when the Golden Gate Bridge gets hot, it sits low in the saddle? Course you didnt: You dont have a Bridge Thermometer, which looks like one of those scenic coin-op binoculars crossed with a first-person shooter. Peer into it (no coin needed!) and it shows the temperature of the bridge and, as a result, how low-slung or high-riding it is; if its 100 degrees out, youll find the bridge has dropped a full 12 feet. Only one BT exists, and the Outdoor Exploratorium has it. The Exploratorium folks made it themselves, of course, along with 19 other exhibits that take advantage of the immediate environment: the crazy winds, the roll of the waves, the organisms stuck to the pier pilings, the salinity of the water (which you can sample). All of them sit around Fort Mason. We particularly like the Wave Oscilloscope, which attaches a stylus to a loose piling, imprinting the sway of the waves into a container of sand, as well as the giant Wind Arrows, which confirm your assumptions that our bay winds are all schizophrenics bent on multidirectional anarchy in the low sky. Grab a map either at the Exploratorium or at Fort Mason Center, Building A, (Marina and Buchanan), S.F.