the tours to the mainland are all day events. pick what you want to do. personally, if i want to do the nature thing, we split the trip 3 days mainland, 5 days island. so i never did a tour out of AC.

that said, i understand the lamanai tour is really cool. i think you boat quite a bit to see the birds etc, then visit the lamanai ruins.

if you can get this link, here is a collage i made of mainland pics i took myself:

http://www.pbase.com/image/3737764

good luck!