Last August we did the Lamanai trip from AC via the tour thru Tropic Air. You leave early morning and fly into a sugar cane field, are transported by van (5 min) to the river and take a leisurely tour to the site (as the guide points out interesting flora and fauna). Early arrival means no crowd; we saw maybe 10 other travelers at Laminai (some menonites). We pretty much had the place to ourselves.

After lunch, a quick boat ride back to the field, and before you know it, you're back in AC by 1:30-2pm.

It was awesome.