PS to Mike,
I don't think anyone could make the lighthouse at the north end and back in one day. The big ruin, El Castillo, is the one that I think might be possible on a day hike. Again the foot trek to Hanan should be pretty easy on the "road", but the extra 4 km round trip to El Castillo may be a problem as your only choices are along a very rough and rocky beach (some sandy places), through dense jungle, or croc infested swamps. Do we have any Steve Irwins out there?
Dave Dillehay
Aldora Divers
PS I have considered tourist/snorkel day trips over the north end in our big boat but have not figured out if there is a market for what it would cost...maybe $150 a head.