Gunungsitoli is the largest town on Nias, with the island's airport, main port, and most of the practical infrastructure — banks, hospital, supermarkets. It is not a beautiful place; most of the older buildings were destroyed in the 2005 earthquake and subsequent tsunami, and the rebuilt town is largely modern concrete.
The reason to stop is the Museum Pusaka Nias on the southern edge of town — easily the best introduction to the island's culture before heading south. The Sunday morning market is busy and worth a wander for the produce, the bargaining, and the chance to hear the Nias language spoken among the stalls.