In Apenheul (near Apeldoorn, The Netherlands) the monkeys run free and the visitors are confined to paths. They used to allow visitors to pet the animals, but in 2006 there were signs that said not to. (The signs were in Dutch and I didn't see them until after I'd pet this lemur.)
The Cologne Zoo has a big collection of lemurs. Their ring-tailed lemurs were allowed to roam free, too, but it wasn't easy for visitors to get close to them. They were affectionate with the keeper, though, and when she went into their indoor enclosure they sat on her lap. This is from my 1997 pencil sketchbook.
The two following drawings are lemurs from Apenheul and are done in colored pencil.
And a final ring-tailed lemur in watercolor. Lemurs are some of my favorite animals (do I say that about every animal I post?) and I hope to see them in Madagascar some day. Soon.