To enter most cenotes, you must typically shimmy down ropes that dangle above the sinkholes and then jump into the cold water. However, visitors can walk right into Rio Secreto, a big plus. You can cross over, walk through streams and sometimes swim across them, heads about one foot from the cave ceiling. In the cave, stalactites and stalagmites grow in thick columns and wide, drapery-like formations, as well as form clusters called “popcorn.” You’ll also note colorless fish in the ponds. The tour is a memorable, underground river experience. Children must be at least 6 years old and be able to swim.