For a place with such an interesting and large collection, it is astounding how low they've set the bar for animal welfare and--especially--aesthetics. What a train wreck.....
Patas Monkey is an open grassland species- slender and graceful- but this looks like a Fort Knox -type building with solid walls strong enough to house a much more robust species. An open grassy enclosure with a small hillock/knoll and a couple of small/dead trees as lookouts would be ample, they could probably just use a hotwire fence to contain them.
What I find peculiar is the imaginative use of words which accurately describe the animals' natural habitats e.g. plains, plateaux, forest but which actually highlight how unnatural the enclosures are! They would be better not using these names IMO.
It does seem to me an excessive amount of building work and cost to house an open grass-dwelling Monkey species- the boardwalk corridor, walls and viewing windows must have cost a lot too and seem to add nothing to this display. I wonder if Colchester authorities have ever watched film of (or observed) this species in the wild?