The largest Maya site in Belize is Caracol. A Classic Maya city, Caracol was a huge city-state with a population of over 80,000 people, thousands of structures, including pyramids, palaces, houses, roads, and extensive fields for farming. As with many Maya sites, after Caracol was abandoned, the jungle crept over everything, and even today only a small part of the ruins have been excavated.

Tip: Visiting Caracol. Only a few lodges are close to the site, and it's a long day trip to Caracoal from San Ignacio, 2+ hours each way on mostly bumpy dirt roads. You'll need to book a tour, and travel on a set schedule to and from the ruins. Going to Caracol is a unique experience, it's so remote and in the middle of the jungle, but it's best with older kids, not little ones.

Before heading out to the ruins, go into the small visitor center to see a scale model of the complex, reconstruction drawings, photos of the tomb burials, explanations of Maya glyphs on the stelae and altars, and several impressive Maya clay vases. Outside the visitor center is a shaded picnic area and restrooms.
Caana - Walk through the jungle to Caana ("sky house"), the largest pyramid at Caracol and tallest building in Belize today. Climb up the steps to the first level. Go left down an open corridor, then turn into an open room with two kid-sized doorways at each end (kids can crawl through the doorways). These small door openings in the residential complex may have been used by dwarves.
Go up the next set of stairs, and plop down on two benches on either side. Kids can rest here just the way the Maya did before they were invited to see royal personages. Walk across the grassy plaza, you'll see a large circular stone. Underneath that stone was buried a royal woman (archeologists dug up the burial, then covered it back over). To the right is a small tomb, with tiny bats flying in the room overhead. You can walk down into the dark room, bring your flashlight.
Walk around to the right, where you'll see a frieze (replica) covered with glyphs. This frieze commemorates the victory of Caracol over the great city-state of Tikal in 562 AD.
Next, hike up the third set of stairs to the top of the pyramid. There's 360 degrees of the jungle in every direction. In the time of the Maya it wouldn't have looked this way - much of the land around the complex would have been cleared and farmed.
Archeological camp - Wander through the permanent camp, where archeologists live and work during the field season. Under an open enclosure are impressive stelae and altars from Caracol, covered with glyphs and figures of Maya rulers and their captives.
Reservoir - Don't miss the reservoir, covered with green plants, turtles swimming around. This reservoir was dug by the Maya hundreds of years ago, and still provides water for the archeologists.
Trees of the Maya - In the forest around the ruins are trees important to the Maya. Twin Ceiba trees are 400 years old, a single large tree is 800 years old. The Ceiba tree, "tree of life," was sacred to the Maya, its gigantic roots connecting to the lower world, the trunk and branches reaching to the upper world. The cohune palm nuts were used for cooking oil, the branches for thatching. The Maya burned the berries of the copal tree for incense.
Rio On Pools - After visiting Caracol, tours usually stop at the Rio On Pools. Bring your swimsuit for a cooling dip in the river, it's a great place to play under the small waterfalls and in shallow pools. Changing rooms are available.