From the World Heritage inscription:
Masada is a rugged natural fortress, of majestic beauty, in the Judaean Desert overlooking the Dead Sea. It is a symbol of the ancient kingdom of Israel, its violent destruction and the last stand of Jewish patriots in the face of the Roman army, in 73 A.D. It was built as a palace complex, in the classic style of the early Roman Empire, by Herod the Great, King of Judaea, (reigned 37 – 4 B.C.). The camps, fortifications and attack ramp that encircle the monument constitute the most complete Roman siege works surviving to the present day.
Masada is in the middle of nowhere, but it was really in the middle of nowhere thousands of years ago. The dry conditions and the remoteness of the location has preserved some elements of the area extremely well. From the top of the mountain you can clearly see the wall (berm) the Romans created to encircle the mountain, the areas set up for their camp, as well as the ramp they built up the mountain.
It is a popular vacation spot for Israelis, especially for boys having their Bar Mitzvah. There is a hostel at the base of the mountain which mostly caters to large tour groups and an excellent museum with interpretive center.