The Actun Tunichil Muknal tour in the most famous tour / trip in Belize. It's a 30 - 45min hike through the jungle followed by several hours romping around dark corridors and tunnels used by the ancient Maya for sacrifices and rituals. Strewn about the place are skeletons, pots and variety of other remnants of ages past.
Difficulty: You really should be moderately agile to go on this tour.
The Barton Creek Cave tour is one of the easier tours. As an added bonus, you'll pass through a Mennonite Village on the way. Once you are at the site you'll get a light, a life jacket and be taken to the canoes. There are Mayan remains, a really old bridge but the most impressive thing about this cave are the formations.
Difficulty: This tour is suitable for pretty much anyone.
This tour is a bit off the beaten path. You'll be heading to Twin Caves in Mountain Pine Ridge. It's a locally known, non-tourized cave system. It takes about 3 hours to worm your way through the various rooms, chambers and tunnels. When you re-emerge into the light, there's a stop by Rio On Pools or Big Rock Falls.
Difficulty: You don't have to be super fit, but size and flexibility do matter.
The Cave Tubing tour takes place at Nohoch Che'en Caves Branch Nature Reserve. It begins with a 45min hike in and then a nice float back out. It's a gorgeous cave system on a slow moving river. There aren't any rapids, but in parts the cave celling is quite low, so you have to wear life jackets and helmets. This trip is more for the caves than the tubing.
Difficulty: The only hard part about this tour is the 45min hike in and out.
The River Tubing tour has two parts. The first of which is the Mayan ruins Xunantunich in Soccutz, Belize (just out side San Ignacio). From there you get in the river at the base of the ruins - The Mopan River. You'll float 3 hrs down stream. You'll hit rapids, see 6ft iguanas, and have large amounts of fun.
Difficulty: This tour is good as long as you can swim and don't mind falling out of your tube.
The Canoeing & Kayaking tour is actually two different tours. Canoeing goes up stream on the Macal to either Chaa Creek or the Botanic Gardens and butterfly farm. Kayaking is done on the Mopan River and goes down stream from the Guatemalan border to a small village named Calla Creek.
Difficulty: These are both good for anyone who likes water and wants to see a Belize without people.
The Cahal Pech & Xunantunich tour combines the Mayan sites of Cahal Pech and Xunantunich. They are the two nearest largest sites near or in San Ignacio, Belize. Xunantunich is the pre-lunch tour and Cahal Pech is the post-lunch tour. They are both great sites and quite different.
Difficulty: Both sites are easy to get to and can accommodate people with some disabilities.
With the Caracol tour you'll be seeing the largest Maya site in Belize and Mountain Pine Ridge. You'll start with a fairly bumpy ride to the back of Mountain Pine Ridge, where Caracol is located. After touring Caracol, there are stops at Rio Frio Cave, Big Rock Falls and Rio On Pools. This is a tour to get a feel for the San Ignacio area.
Difficulty: The road is very bumpy and there will be some hiking.
The Tikal tour is a speciality of Maximum Adventure Tours. There is an overnight trip and a day trip. The day trip leaves in the morning, takes you across the border and into Guatemala 4hrs at the site and then back to Belize. If you want to overnight it, you'll get the Sunrise tour and the Sunset tour.
Difficulty: This tour is spectacular and can be done by anyone.
The Mountain Pine Ridge tour is a fantastic place to get away from people for a while. It's made up of 3 parts (for the most part) - Rio Frio Cave, Rio On Pools and Big Rock Falls. There are other great spots too, but these are the crème de la crème. There's swimming, hiking, and cliff diving (if you want).
Difficulty: It's not a super tough tour, but there is some hiking and very bumpy roads.
On a very large number of the jungle hikes you will go on in Belize, you will be offered termites to eat. It's a tradition for Belizeans to offer guests to their homes the carrot or mint tasting varieties. It's also a little on the rude side to turn them down, unless you are a vegetarian. Even that's a grey area for some.
Difficulty: This is a great for anyone with a hang over or who wants a good story.
Zip-Lining can be done in two places near San Ignacio, Belize. The first and closest is on the Hummingbird Highway at a place called Jaguar Paw. You can also go Cave Tubing at the same place. The second place is in Guatemala, right near Tikal and is usually combined with the regular Tikal tour. Both trips are equally awesome.
Difficulty: Size and agility are the main factors in regards to Zip-Lining.