Halmstad's proximity to the coastline means that there are some great natural sites on offer, but with galleries and historical locations available as well, you'll have plenty to spread your time between. If you hire a car from Halmstad Airport you can head straight into the city. It's divided in two by the Nissan River which is edged with some great trails and running areas should you get the chance to explore. Halmstad is home to many beaches and the Östra Stranden beach is particularly family friendly.
Halmstad has plenty of historical landmarks and museums which are worth visiting. Halmstad Castle dates back to the 17th century and has Danish roots, having been built when Halland was part of Denmark. As an official building, the interior is not open to the public, but the courtyard often hosts summer theatre productions and a Christmas market.
Based right on the edge of the city, hiring a car from Halmstad Airport is a great way to start your adventure through Sweden. The Mjellby Konstmuseum is worth a trip if you're an art enthusiast. The museum is based on six local artists who were influenced by Magritte and Dali and pushed the boundaries of French Cubism and Surrealism in the 1920s and 30s.