I don't know anything about the Glencar Inn except that I saw a notice that there are sessions there on Thursday nights from 10-12 pm

The same poster, which I've just seen at Letterkenny's Grianan Theatre, also listed the following sessions in Letterkenny all from 10-12 pm:
Mon.- Brewery Bar, Market Square
Wed. - Central Bar, Main St.
Thursday - Swilly Inn, Gortlee (on the outskirts of town, I think in the Ramelton direction; Glencar is also a bit outside the town centre)

I cannot vouch that these sessions are all current and on the nights stated; do check with the pubs beforehand.

I believe there is set-dancing at the Lagoon in Termon on Monday nights.

there will definitely be music at the Mount Errigal hotel and the Holiday Inn this Sat night 30 Oct 2004, at the Oireachtas festival club (Club na Féile). Also at 7 pm there will be a sean-nós singing competition at the Mount Errigal (& broadcast on RTÉ Raidió na Gaeltachta), and from 10 pm a room will be be set aside for a singing circle, "Club Amhránaíocht ar an Sean-Nós".