Complex sentence: The concrete remains of part of this facility can still be seen on the summit of the hill: the octagonal concrete base measures 3.85 m (13 feet) across, with a channel running west to east across the middle.
Split into simpler sentences: The concrete remains of part of this facility can still be seen on the summit of the hill. They consist of an octagonal concrete base that measures 3,850mm across, with a channel running west to east across the middle.