In Calistoga where hot springs bubble under the surface, Old Faithful Geyser is one of the state’s most photographed places. Powered by natural geothermal pressure of a subterranean volcano located just two miles from downtown, rainbows form in the misty spray that faithfully erupts up to a height of 60 feet every 15 to 30 minutes. Children love it. Learn how geysers work at the Geology Museum, have lunch in the picnic grounds, visit the petting zoo to see llamas, horned sheep, and mountain goats. The geyser site is open every day, but there is an admission charge. oldfaithfulgeyser.com<