Aktun Chen was Leroy and my first tour in Mexico.  It was offered free through El Dorado Royale Resort (now called El Dorado Seaside).  We walked through the underground cavern.

On this trip we decided to take A snorkeling, since we had never snorkeled a cenote either.  What a wonderful snorkel!  We shared the cenote with one other couple and had a great day playing in the cavern.