These concrete "mountains" are still fairly common in zoos, particularly throughout Europe, and in most cases the enclosures were constructed many decades ago. Other than their almost complete lack of natural substrate, these mock-rock boulders often become scorching hot in the summer and thus totally inappropriate for their occupants.
@snowleopard: How many zoos in Europe have you actually seen, BTW?
I can't believe that someone would actually keep lemurs on a rock like this, especially ruffed lemurs and black lemurs which are both highly arboreal species. This shows a complete disregard for the animals' biology and behaviour and I could think of many monkeys more suited for this type of exhibit.
