Denver Zoo

It's a 130 year old zoo, so obviously not a dedicated wedding venue, but they do run private after-hours social events with the animals as the backdrop, a fun angle if you want something other than a hotel ballroom. Reviews are mostly general zoo-visit ones rather than weddings, though one recent 5-star mentioned a bomb threat evacuation during their visit that they felt was handled with confusing communication from staff, the kind of thing I'd want a straight answer on before planning a private event there. Otherwise very high marks across the board for cleanliness and staff friendliness.