20 miles N of Provo, 35 miles S of Salt Lake City
This national monument is actually composed of three caves -- Hansen, Middle, and Timpanogos -- that are linked together by man-made tunnels. Martin Hansen discovered the first cavern in 1887 while tracking a mountain lion. The other two were reported in the early 1910s, and the connecting tunnels were constructed in the 1930s. The caves are filled with 47 kinds of formations, from stalactites and stalagmites to draperies and helictites. The caves aren't easy to reach, but their beauty and variety make them worth the rough 1 1/2-hour trek to the mouth.