Complex sentence: There are many circular depressions within the enclosure, and at least 20 are probably contemporary storage pits; there are at least 30 platforms arong the perimeter, which are thought to be huts.
Split into simpler sentences: There are many circular depressions within the enclosure, and at least 20 are probably contemporary storage pits. Around the perimeter are at least 30 platforms, which are thought to be huts.