Prague Zoo is absolute world-class. It's massive, beautifully built into the hillside in Troja, and…read morethe enclosures feel very modern, spacious, and natural. The Elephant Valley and the Indonesian Jungle were absolute highlights.
Be prepared for a lot of walking--wear comfortable shoes! There's even a fun little chairlift inside the park to help you get up the hill, which offers great views. Everything is clean, well-maintained, and there are plenty of places to grab a bite or a cold beer.
Pro tip: Buy your tickets online in advance to completely skip the morning queue at the entrance, and aim to arrive right when it opens.