Hanna Stables horseback ride to Xunantunich has become one of the more popular tours around Cayo. Add a stop to Benny's Kitchen for lunch, and you have the perfect half day tour. Santiago is definitely the horse whisperer.
https://www.facebook.com/media/set/?set=a.10151669721471162.1073741885.265387546161
http://www.hannastables.com/horseback-riding-tours/
"The ride to Xunantunich is pleasant and scenic, including the crossing of the Mopan river by a hand-churned ferry. Just a little further on are the well known Mayan ruins of Xunantunich. Also, if it’s a lucky day, you will be able to experience an up close encounter with howler monkeys.
The Xunantunich ride has a duration 1 ½ hours of riding to the site and approximately 2 hours hiking of the site, and an additional 2 hours ride back. This is a half day to a full day ride depending on the request of the guest. Lunch stops can be included to a feast of local dishes in a pristine setting along the river. Please indicate in the booking form if you would like lunch included."
They have 55 perfect reviews, and 2 great reviews on Trip Advisor.
http://www.tripadvisor.com/Attraction_Review-g291971-d2441112-Reviews-Hanna_Stables-San_Ignacio_Cayo.html