Lake Bled is a 2 km-long glacial lake in the foothills of the Julian Alps. Perched on a cliff above the eastern shore is the 11th-century Bled Castle, and on the island in the middle sits a baroque Church of the Assumption, reached by traditional wooden pletna boats. The walk around the lake is 6 km, about an hour to ninety minutes at a relaxed pace. The town is tiny – everything is within walking distance. Four kilometers north lies Vintgar Gorge with wooden walkways above the river.
From Ljubljana, buses to Bled cost €6–8, depart every 30–60 minutes, and take 1 hour 15 minutes. The bus stop is a 3-minute walk from the lake. The train goes to Lesce-Bled station (€5–10), but that's 4 km from the lake – you'll need another bus or taxi. There's no direct bus from the airport: transfer in Kranj or Ljubljana. If you're heading further to Kranjska Gora or Bohinj, renting a car will save hours. One day without rushing is doable, but staying overnight is better – mornings and evenings see a fraction of the crowds.
