Sebastia was once the capital of the northern Israelite kingdom of Samaria and as such a major city around 700BC. In 332BC, it was captured by Alexander the Great, and it was handed to King Herod in 30BC. In the 2nd Century, the city became known as the site of John the Baptist's burial. The city was also captured by Islamic forces in 634 as well as by the Crusaders, who built a stunning cathedral that is now a mosque. This is only part of the story... but it shows how rich this quaint town is, and how important for religious pilgrims from all walks of life!
What I liked most about Sebastia was the absense of tourists, which was refreshing and unusual. However this also sadly means that the area is not as protected as it should be and thus many columns and other artefacts regularly go 'missing'.
Sebastia is about an hour north of Ramallah by taxi, and there are plenty of accommodation options there. It is worth staying for at least one night to discover the archaeological site and to hike in the surrounding area. Combine with a day trip to Nablus as well.
More info here:
An article by the Electonic Intifada describing the political situation there