Mayan site in Cayo Belize district.
120,000 up to a 180,000 population at its peak.
I had my resort arrange this tour. I think it was around $100. After Caracol, which was a half day tour, I went swimming in a lake and visited a cave.
It is better to use a tour guide. Getting around Belize is a little tough. Most of the roads are not paved and rough. Expect to be bounced around.
Scroll to the bottom, video of howler monkeys (only hear) and walking around the top of the temples.
You you can hear the howler monkeys. They sound like a T-Rex! Or at least, this is what they use for the movies.