Slovenia is a small country that has some big beautiful scenery. Its two most famous lakes are Lake Bled (the more popular) and Lake Bohinj. Lake Bohinj is about an hour's drive from Ljubljana, the nation's largest city and capital, and a 30 minute drive from Lake Bled.
There's a lot to recommend a visit to Lake Bohinj over Lake Bled, although by all means visit both if you have the time. The lakes are separated by only 26 kms of lovely mountain scenery, and it's easy to drive from one to the other.
Bohinj has a more natural setting that Bled, with less development and fewer tourists. It is surrounded by the grand Julian Alps and Triglav National Park (the only national park in Slovenia, but a beautiful one).
There is no town known as Bohinj; the name refers to the glacial valley in which the lake is located. The lake covers 318 hectares (790 acres), is 4.2 km (2.6 miles) long, and is the largest lake in Slovenia. Ribčev Laz is the small community where you find services at the lake, with several other smaller villages nearby.
The outflow at the lakes eastern end is through is the Jezernica River, which you can cross on a nice arched bridge. This bridge provided last Saturday's One Clue mystery, and was recognized by the incomparable GeorgeG.
More water leaves Lake Bohinj than enters it because of subterranean sources of water (aquifers). The clear waters of the lake are over 40 m deep and are home to brown trout, burbot and Arctic char.
The area is a very popular destination for those who love outdoor activities throughout the year. It's most busy in the summer when activities include swimming (though the water is never very warm), fishing, kayaking, canoeing, wind-surfing, hiking, and mountain bike riding. A cable car adjoining the lake goes up Vogel, a mountain which offers great views of the region -- we were interested in doing this, but it was a cloudy drizzly day -- not a great one for exploring the subalpine -- so we moved on. There are some popular hikes, including to a waterfall (Slap Slavica) and gorge.
A boat tour around the lake runs in the summer months. Boat rentals are also available.