Arrochar and Tarbet Station is on the West Highland Railway and is served by about 3 ScotRail  trains per day heading North from Glasgow Queen Street and South from Mallaig, Fort William and Oban. ScotRail also operate a sleeper train from London Euston to Fort William via Tarbet six nights per week.
Tarbet is served by Citylink  buses going from Glasgow to Fort William, Skye, Oban and Campbeltown. Note that all of the buses heading for Campbeltown also serve Tarbert (Loch Fyne), so make it clear to the driver that you want Tarbet on Loch Lomond.
The village would take about 10 minutes to explore on foot.
Bed and Breakfast