Hi Chris,
Ahh a fellow enclosure fan!. (Are we both mad!)
I'm no expert on the Cornish Language but a quick search on the web finds that "Car" or "Caer" in Cornish is a place name from the Celtic "ker" meaning fort.
The beauty is that Cornwall is full of em! - singles, doubles, also we have cliff castles, hillforts not to mention Plain en gwarries!
I have found the following "Caer" sites on the map but haven't had chance to visit them yet.
Caer Dane
http://www.themodernantiquarian.com/browse.php?site_id=737
Caer Keif
http://www.themodernantiquarian.com/browse.php?site_id=738
Caer Vallack
http://www.themodernantiquarian.com/browse.php?site_id=782
Anyone who plans a visit to Cornwall's cool landscapes be sure to try and get your hands on the following books. Most librarys in Cornwall would have a copy and I have seen them in certain bookshops.
"Cornovia - Ancient Sites of Cornwall and Scilly" by Craig Weatherhill £9.50 (Out of Print). ISBN: 1871060311 and "Belerion - Ancient Sites of Land's End" by Craig Weatherhill (Alison Hodge, Paperback, £3.50 (Out of Print). ISBN: 090672001X
Both books give a comprehensive guide to the ancient sites of Cornwall and the Isles of Scilly, both are illustrated with line drawings and with full access details
Phil
Near Castle an Dinas, (The Goss moor one), Cornwall.