This is a must-do experience in Rio. Sugarloaf Mountain is a nakedly commericial venture, so be prepared for a lot of shops and food outlets, but the views from the top make it worthwhile and, beyond the cable car ticket, you don't have to buy anything...
If you can afford it, get the skip the line ticket. It works on the way up and the way down and can save you hours, literally. It can be busy but to see the scale and beauty of Rio and its setting, it's peerless.