Ik Kil is a dramatic open-air cenote that many visitors combine with Chichén Itzá, so expect crowds unless you arrive at opening. Bring a swimsuit, towel, water shoes for the wet, steep stairway, and a small waterproof bag; lockers, changing rooms, showers, and life jackets are available for rent, and the water is deep so use a jacket if you are not a strong swimmer. Pay the entry fee on arrival (cash is easiest), rinse off biodegradable sunscreen before you get in, and be ready for a strenuous climb back up the steps — it’s not very accessible for those with mobility limits.