Nothing's better than relaxing by the water while you're on vacation. Take a picnic to Avis Dam and then hang around for an impressive sunset.
You're spoiled for sightseeing choice in Windhoek. Avis Dam is a great place to start here, but there are lots of other fine spots to explore. NamibRand Nature Reserve, Maerua Mall, and Christ Church are close to the body of water and will round out your day nicely.