I’ve had two trips to Ireland. Second one, in 2018, was with rental car, and went north. First one, 2011, was by touring bicycle, but we had 3 weeks, and were flying home from Shannon, not Dublin. But we used the national bus line, Bus Éireann, when we weren’t pedaling. The buses have an Irish Setter on the side, instead of a Greyhound.
So how all this fits into Portmagee or not: partly to avoid extra time and pedaling as evening was approaching, I stayed overnight in Cahersiveen, a few miles before Portree. The morning of my hopeful Skellig Michael boat trip (they decide that morning whether the seas are too rough for the crossing, or if they’ll be able to go), I hopped on the bike, and rode the short distance to the very short ferry from Reenard Point to Knightstown at the western tip of Valentia Island. My boat captain, who I believe has now retired, lived up there, and gave me a place to stash my rental bike, then a ride to the boat docks to await the decision whether to sail or not. We went, and the Skelligs are awesome!
But going to the Bus Éireann Website just now, https://www.buseireann.ie , it seems they don’t go to Portmagee, but they do go to Cahersiveen . That would get you in the area, but a taxi or other arrangement might be needed -even a bicycle rental in Cahersiveen for the day?