Killadeas island week: Lower Lough Erne, Devenish, Boa Island and Belleek

Manor House Marine, a family firm for more than 50 years, keeps its fleet in a basin enclosed by land. After the handover, run south for just over an hour to Devenish Island, the Erne's great monastic island, founded by St Molaise in the 6th century. Its round tower, about 25 m tall, is one of the finest in Ireland and the only one with a carved cornice under the cap, and the graveyard has an intricately carved 15th-century cross. The public jetty is shared with the tour boats and has no services apart from toilets in high season. In spring, keep to the paths: curlew, snipe, redshank and lapwing nest in the grass.

A short hop upstream through Portora Lock, the only lock on the Erne. It is normally open; when the level falls towards 150 ft, DfI Rivers puts the gates into operation and staff work them from 08:00 to 22:30, and if you find them shut, call +44 28 6638 8529. The ruins of Portora Castle stand beside it, and rowers from the Enniskillen Royal Boat Club train on this reach, so keep your wash down. In Enniskillen tie up at the Broadmeadow public jetties in the town centre (toilets and showers). The castle by the river holds the Fermanagh County Museum and the Inniskillings Museum, and Blakes of the Hollow, a Victorian pub of 1887, has traditional music on Fridays.

Pump out at the Round O jetty in Brook Park, then go back through Portora and west along the south shore. Inishmacsaint makes a good lunch stop: the church site goes back to St Ninnid in the 6th century, and its ruin, built in two periods, stands beside a tall, almost plain stone cross about 4 m high that local legend says turns three times on Easter morning. The jetty is the only official way onto the island. Under an hour on, Tully Castle has its own jetty below the walls of a planter's house burned in the 1641 rising, with restored gardens, a free cottage exhibition, toilets and the waymarked Tully Castle Walk along the shore.

The open-water day. Follow the south shore under the Cliffs of Magho, a limestone escarpment about 9 km long, and stop at Magho jetty beside a car park with toilets. A steep path of about 2.5 km, graded difficult, climbs through woodland to a viewpoint over the whole lough to the Sperrins, the Blue Stacks and Slieve League. The cliffs face north-north-west across the open lough, so only stop in a light wind. At Rosscor Viaduct the lough becomes a river again: we have found no published clearance for its spans, so keep to the marked passage and go slowly. Belleek has a public marina with toilets, showers, a pump-out and a slipway, but no shore power.

Belleek is the end of the navigation. Start at Belleek Pottery, Ireland's oldest, where the visitor centre is free and guided tours of the workshops leave every twenty minutes (small charge). Then head back east along the north side of the lough to Lusty Beg, a private island resort beside Boa Island. Space at its jetties goes first to diners and guests, so ring ahead to dock and dine (+44 28 6863 3300). The resort's free ferry crosses on demand to the Boa Island shore for Caldragh graveyard and its two carved stone figures, the double-bodied Dreenan figure and the smaller Lustymore figure. Finish up the tree-lined Kesh River to the public marina below the road bridge in Kesh.

Restock in Kesh's shops in the morning, then head out of the river and south to White Island in Castle Archdale Bay. Against the north wall of its ruined church of about 1200 stand eight carved stone figures from the 9th or 10th century, and the late Romanesque south doorway is the only one of its kind surviving in Northern Ireland. Moor at the island jetty; the land outside the church walls is farmed. A few minutes across the bay, the Castle Archdale forest jetty is a public mooring near the old castle ruins; the marina there is private with little visitor space. The holiday park's shop, chippy, restaurant and bar keep seasonal hours.

Spend the morning in the country park. A small museum in the old courtyard tells the story of RAF Castle Archdale, the wartime flying-boat base whose Catalinas helped find the Bismarck in 1941, and waymarked trails run through about 520 hectares of woodland and lakeshore. Then cruise south along the east shore, about two hours, back to Killadeas. Before you hand the boat back, walk to the old churchyard by the road to see the Bishop's Stone, an early-medieval carving of a cleric with a bell and crozier. The Enniskillen RNLI lifeboat station and the Lough Erne Yacht Club, on the site of the wartime RAF Killadeas base, are on the same shore.