The Park Service co-sponsored this year’s International Congress of Speleology (ICS), which has been going on all week in Kerrville, Texas. Many of the 1,300 participants signed up for field trips that included guided tours of developed and wild caves within NPS units.

South Dakota’s Jewel Cave National Monument, which celebrates its 101st birthday today, offers convenient access to underground beauty and the world’s second longest cave system. While it hasn’t always been easy for the public to enjoy Jewel’s scenic wonders, visitors today have three great tours to choose from. Be prepared for a tight squeeze if you choose the Spelunking Tour.