We went to Tulum. Luckily no one acutally got sick, even though we had two that we thought would. Keep your eyes on the horizen you should be ok. But we also waited to see the weather too so we wouldn't have the choppy sea thing going on. I heard Belize is alot of travel too although not the mainland trip. Either way you'll have to devote one day to the trip. It was worth it though.
I was shocked at how easy it was to get to Tulum. It is a straight 4 lane highway from the port to Tulum. One could easily do without a tour group.
Carnival Fantasy 6/05
RCCL Sovereign of the Seas 4/07
RCCL Navigator 12/07
RCCL Navigator 11/08
RCCL Liberty 7/4/09