The ship is the best way to go for a excursion to the mayan ruins in Belize because everyone on your ship will be there and the tour guide will be in touch with the ship if something happens. The ship anchors a fair distance out and you go on a speedboat tender to the cruise center where the shops and tour buses meet.
Altun Ha is a smaller site than Xunantunich. I do believe both sites allow you to climb the temples/pyramids. The problem with going on your own is you have to watch the time as you only have some much port time. Xunantunich is a LONG drive and it takes over 2 hours to get to the site. The tour is 7 hours and you get back in time to jump back on the tender back to the ship. Altun Ha tours are around 4-6 hours and you get a thorough guided tour through the site.
I did the tour through the ship and it was perfect. I do suggest bringing at least 1L of water if you are going. Belize is HOT!!!!
One other note is the roads in Belize are OK, but when you turn off the "North highway" to the old highway the road is rough, very rough and if you breakdown you might be there a while.....I can tell you the old highway is nothing more than a 1.5 lane rough gravel road, with barely any gravel left, no shoulder, and the forest very close to the edge of the road.....
2007 Victory & Triumph
2008 Conquest & Liberty
2009 Valor, Freedom, and Splendor
2010 Glory and Liberty
I gotta go where it's warm.....
Over 40 victim of fate.....