While other couples sport stilettos and wing tips for a night out, your excursion will have you in helmets, boots and knee pads At Lava Bed National Monument in northern California, you can take a three-hour tour of the Crystal Ice Cave to see spectacular ice formations. This spelunking adventure will have you descending ladders, ascending sloped ice floors with a rope and crawling through tiny spaces. Although it's $10 to get into the national monument, the tour is free. Make sure to make a reservation. Space is very limited.