Machu Picchu was our most difficult excursion. Our hotel had no elevator, but the staff carried my wife upstairs which gave her access to a small cement floor from which she could view part of the ruins.
I could also push my wife to the formal entrance from where we had an additional overview of the field of ruins. We could enter beyond the entrance for only about a hundred yards at best then the paths became too narrow with at times big steps.
We did fine as far as the elevation was concerned as we took two days in Cuzco to get used to it. A slow approach to acclimating to higher elevations is definitely recommended.
While in Cuzco, it was an easy trip with a sightseeing van to the fortress of Sacsayhuaman which is quite impressive. It is built with tight-fitting rocks the size of a dishwasher to the size of a passenger car. The bus parks at a spot that gives a good view so it isn't necessary to hike around those blocks to get an idea of it. Grazing llamas might visit.
We visited Petropolis, the summer capital of the Brazilian emperors. with our rental car and stayed one night at the Riverside Park Hotel, Tel: (0242) 43-2312. This is a quiet, older hotel in a large park, and it was the only hotel we encountered that catered to wheelchair users in a specific way. The staff brought pre-cut wooden planks and placed them in strategic places to make the place fully chair compatible.
Registro is one of the few stopover places when you drive a car from Sao Paulo to Curitiba. The hotel in Registro, the Estoril Palace Hotel, has no elevator. It has the ground floor for the restaurant and one upstairs floor. It also has about four to five motel-like rooms that require about 100-200 yards of walking.