McDermott's Castle
Caisleán Mhic Diarmada
Ireland · County Roscommon · Near Boyle
Built 1180 · Island castle ruin — Norman origin, 12th century foundation on a natural lake island; rebuilt and extended by the MacDermott-Roe dynasty through the 14th–17th centuries; the surviving structures include curtain wall fragments and a square tower; the island setting is the defining characteristic
This page is part of an independent travel guide and is not affiliated with, endorsed by, or operated by McDermott's Castle.
© Castles & Palaces
Quick Facts
- Hours
- Closed Mon–Sun
- Boat tour from
- €22
- Duration
- 1.5–2 hours (boat tour from mainland)
- Best time
- May to September
- Nearest city
- Boyle
Featured Tour
Roscommon: Lough Key Boat Tour with Guide — Views of McDermott's Castle
Cancellation available · Instant confirmation
Highlights
- ✦Castle Island setting — McDermott's Castle occupies its own island on Lough Key, accessible only by boat, giving it one of the most romantic silhouettes in Connacht
- ✦Guided boat tour of Lough Key — the castle is the focal point of a scenic cruise that covers the lake's 33 islands and their history
- ✦MacDermott dynasty history — lords of Moylurg (north Roscommon) for 500 years, patrons of the Annals of Lough Cé (one of the most important medieval Irish annals), and the last Gaelic family in Roscommon to maintain a hereditary castle
- ✦Lough Key Forest Park — the former estate surrounding the lake, now a woodland activity park with a bog garden, tree canopy walk, and archaeological sites on the mainland shore
- ✦Romantic tragedy of McDermott and Mary Cormac — a 19th-century island love story that became one of the most famous in Irish tradition
Skip the queue with a guided tour
Skip-the-line tickets & expert guides
McDermott's Castle stands on Castle Island in Lough Key — a 33-island lake in north Roscommon surrounded by one of Ireland's most beautiful stretches of Atlantic woodland. The castle is a ruin: curtain wall fragments and a square tower survive on the island, together with the remains of a small church. What makes the site exceptional is its setting — the castle on its private island, reflected in the dark water of Lough Key, with the forested hills of Boyle surrounding the lake, constitutes one of the most atmospheric medieval landscapes in the west of Ireland.
The island is not accessible to independent visitors — there is no public landing stage, and the castle ruins are not maintained as a visitor attraction in the conventional sense. The closest legitimate access is the Lough Key guided boat tour (GetYourGuide, t1374909, €22), which offers lake-level views of the castle and island with commentary from a local guide. The tour is framed as a scenic cruise around the lake with views of McDermott's Castle — not as an admission ticket or landing visit. Visitors looking for views from land can access the Lough Key Forest Park on the mainland shore, where the castle is visible across the water from several points on the shoreline path.
History
The MacDermott-Roe family — Mhic Diarmada in Irish, lords of Moylurg (roughly north Roscommon and east Mayo) — established their castle on the largest island of Lough Key sometime in the 12th century, possibly on the site of an earlier Norman fortification. The lake's position — surrounded by woodland and approachable only by boat — gave the island castle an inherent defensive advantage that the MacDermotts exploited for five centuries.
The family were major patrons of Irish learning: the Annals of Lough Cé, one of the most important chronicles of medieval Irish history covering the period 1014–1590, was compiled at Lough Key under MacDermott patronage. The castle remained the family seat through the Tudor conquest and its aftermath, making the MacDermott-Roe lords among the last Gaelic dynasties in Connacht to maintain a hereditary castle. They were finally displaced during the Cromwellian land settlements of the 1650s.
The most poignant chapter of the castle's history is 19th-century: Una MacDermott and Thomas Costello (also told as Mary Cormac and MacDermott) — a love story between a Protestant Irish landlord and a Catholic tenant's daughter, separated by family opposition, that ended in both their deaths and became one of the most celebrated romantic tragedies in Irish oral tradition. Thomas Costello allegedly swam out to the island nightly to see Una; after her death, her father refused to bury her on the island, and Costello died of grief on the mainland shore. Both are said to be buried on the island. The story inspired the poem 'Dark Rosaleen' and is still told by local guides.
How to Visit
Boat tour (recommended approach): The Lough Key guided boat tour (available on GetYourGuide, t1374909) departs from the Lough Key Forest Park marina. The tour is a scenic guided cruise around the lake's islands with commentary on their history, ecology, and folklore. McDermott's Castle and its island are the focal point of the cruise — views are from the water. The tour price is €22 per person and runs April through October.
Note on access: This is a boat tour with views of the castle from the lake, not an admission ticket for castle entry. The island has no visitor landing facility. Please read the GYG listing carefully before booking to confirm expectations.
Mainland viewpoint: Lough Key Forest Park (open daily, entrance fee for the park) has shoreline walking trails from which the castle island is visible across the water. The park itself — formerly the estate of the King family of Rockingham House, whose 1820 mansion burned down in 1957 — has a bog garden, woodland trails, and a tree canopy walk.
Getting there: Lough Key Forest Park is 3 km east of Boyle town on the N61. Boyle is accessible by train and bus from Dublin (via Mullingar). Car is the most practical option for the lake visit.
Frequently Asked Questions
No — Castle Island has no public landing facility and the castle ruins are not accessible to independent visitors. The island is viewable from the lake on the Lough Key guided boat tour (GetYourGuide, €22) or from the mainland shoreline of Lough Key Forest Park. Do not attempt to access the island by private boat without explicit permission.
Location
Castle Island, Lough Key, Co. Roscommon, Ireland
Tours & Tickets
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From
€22/ person