for adventure, i really enjoyed our stay in cayo several years ago. there was lots of adventuring to do. we chose to rent a jeep and tool around on our own.
the ruins at xunantunich & cahal pech are near there, and the next day we went to pine mountain ridge forest to see the 1000 ft waterfall and the caves at rio frio (rio un). that was an awesome day. the cave is HUGE!!!! the zoo was closed the day we got there. we rode horses thru the jungle at banana bank ranch.
i had great fun there (and was a bit beat up to prove it).