It takes roughly 50 minutes to make the 60km drive from Ljubljana, about half of which is motorway, while the remaining half is along country roads that take you through several small villages and get increasingly windy as you near Idrija - if you get stuck behind one of the many school buses plying this route to take pupils to the mining museum, it can add an extra few minutes to your journey. Take the exit to Logatec and follow the 102 and signs from there.
If you're feeling adventurous, or it just suits your itinerary better, Idrija can also be reached via smaller roads over the mountains from Nova Gorica and Tolmin in the east or Žiri and Škofja Loka in west, which are usually kept clear of snow during winter. If you don't have your own car, there are nine buses per day between 08:15 and 19:15 from Ljubljana's main station, although this drops to eight on Saturdays and five on Sundays. The fare is €6.30 one-way, and can be paid on the bus.