We had expected to be on a 13-hour tour today. It had been scheduled well in advance for Monday. The tour operator changed it to Tuesday. Then at 10 pm Monday night he called to say he was sick so we postponed to Friday. Oh, well. We simply improvised and spent the day at 146-acre Xplor Adventure Park. The place is fascinating. Lots of it is underground in a huge network of caves complete with stalactites and stalagmites. We have no idea how many miles we walked underground to move from one activity to another but it seemed enormous. There are 6 activities: zip-lines, amphibious vehicles, rafts, swimming in underground rivers, spelunking and hammock splash. First up was the Stalactite River Swim. The water temperature is "brisk" but we soon became accustomed. We swam/floated/bobbed/walked along an underground river, through amazing caverns with lots of twists and turns for about 400m. We found it a bit challenging. Amphibious Vehicles are basically jeeps. One drives through jungle trails, crossing suspended bridges and goes under the surface into caverns and caves. Then we did the Underground Rafts, again on an underground river through rock formations whose existence has taken millions of years to develop. We sat atop 2-person rafts and used hand paddles that looked like flip-flops. We paddled about 570 meters. The best thing we did, however, was the zip lines. The other Jim opted out and happily spent his time gently rocking in a hammock while the other 5 of us played. There are 14 zip-lines with 3.8 km of trails. The highest zip-line is 45m above ground and the lowest is 8m BELOW ground. We zipped along at 30 km/h, crossed suspended bridges, rode down a water slide, and got drowned by waterfalls and from being dumped into cenotes. We loved it!