duPlooy's (and other vendors) have many different types of tours and trips available. Some are for couch potatoes, some for the very active and fit.
Many of the trips involve and much or as little physical activity as you want. For example, Tikal can be very strenuous if you climb all the temple buildings and do a lot of walking, or you can just ride there in a van and walk casually around the museum and on some of the trails. Probably if someone has a problem walking it would be better not to go on a group tour, but either to walk alone using a guidebook or to arrange a private tour with a guide.
Most trips do involve at least some walking. Xunatunich and Cahal Pech are small Maya sites near San Ignacio that do not require much walking. Che Chem Ha Cave Maya site or any of the other caves such as Barton Creek are probably too strenuous for someone with limited mobility. Rio Frio Cave in the Pine Ridge would be okay, probably.
A visit to either Green Hills or Chaa Creek's butterfly farm would be okay for most anyone, as would a walk through the Rainforest Medicine Trail (formerly Panti Trail) near Chaa Creek.
The grounds at duPlooy's are somewhat hilly, but they are well maintained with walkways and you can drive most places including around the Botanic Gardens.
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