Map: OS of Ireland 1:50,000 Discovery Sheet 12.
TRAVEL: (Two cars) From Castlederg (B72 or B50) follow Killeter signs. From Killeter, follow 'St Patrick's Well, St Caireall's Church'.
Leave one car opposite holy well; continue in other car to T-junction; left on Shanaghy road for three miles (5km).
Opposite small quarry with double gates on right, turn left along rough track ('Causeway Walk'). In 150m park on bend by barrier ('Causeway Hill' waymark).
WALK DIRECTIONS: Yellow arrow points right, but you go left past barrier. Follow The Causeway for 3Â¾ miles (6km). At foot of lane (yellow arrow), left along country road. At 'Mellon's Glen' signboard, detour left through gate. In 50m, right at cross-inscribed stone to Mass altar. Return and continue along road. At T-junction, left and left again up Magherakeel Road. Pass lime kiln and St Caireall's Church to return to St Patrick's Well.
LENGTH: 5 miles/8km: allow 2Â½-3 hours.
CONDITIONS: Very boggy underfoot in places. Boots, gaiters and waterproof trousers advised.
DON'T MISS: Bog flowers; views of Blue Stack Mts and Mt Errigal; Mass altar in Mellon's Glen.
ACCOMMODATION: Marian McHugh, Glen House, 30 Aghalunny Rd, Killeter BT81 7EZ. Tel: 028 8167 1983. Offers drop-off and pick-up at start and finish of walk.
GUIDED WALKS: Martin Bradley. Tel: 028 7131 8473/ 079 2678 5706; martin839@ btinternet.com.
INFORMATION: See walkni.com; discoverireland. ie/walking.
•Tourist Information Centre: Strabane. Tel: 028 7188 4444; discovernorth ernireland.com.
•National Trails Day: October 2. See nationaltrails day.ie.
•Christopher's book 'Walking in Ireland' (Ebury Press) contains 50 of his favourite 'Irish Independent' walks.