Complex sentence: The Castle Arch is a center piece of the old castle grounds, and admits walkers to the demesne parklands; still held in trust as a gift to, and possession of, the people of Macroom.
Split into simpler sentences: The Castle Arch, a center piece of the old castle grounds, admits walkers to the demesne parklands. It is still held in trust as a gift to, and possession of, the people of Macroom.