Lough Rynn Castle Hotel in Mohill is set to more than double its number of bedrooms and to develop a leisure centre.
Leitrim County Council has given the venue planning permission for 51 extra bedrooms, bringing the total to 95.
A leisure centre, with a swimming pool and gym, has also been given the go-ahead.
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Local Independent councillor Enda Stenson says it's a major boost to the area.