When my wife and I went to New Zealand last year, we went swimming at a hot water beach. It was a really fun, interesting experience.
I've never heard of a hot water beach.  What's it caused by?
There are geothermal springs under the water at that particualr beach, and they slowly release hot water into the ocean. When the tide is high, the hot water is carried by the waves onto the shore, so you get this pleasantly warm water to swim in.
Was that the coolest thing that you did there?
It's really hard to pick the coolest thing we did there. New Zealand is an amazing place, and there was so much to do. I'd highly recommend going if you get the chance.