Navarre is the eastern part of the Greater Basque region – the western is the Basque Autonomous Community itself. The most significant cities there are Bilbao, San Sebastian, and Vitoria. Each of these places worth the visit. San Sebastian is the closest to Pamplona (80 km) – you can reach it by car for about an hour drive to the northwest. Vitoria stands on a similar distance (100 km) from the central Navarrese city and lies on the route to the most distant and the most significant Basque city overall – Bilbao. If you want to visit the latter and then come back to Pamplona, better make plans for a multi-day tour.
On the other hand, Bilbao Airport operates much more flights than Pamplona. So if you come to Spain from outside the country, you can land in the heart of Bizkaia, hop on a train or bus to Pamplona, and when it’s time to leave Navarre, you can spend a day or two in Bilbao before you take off from the country.