Bled Castle is hard to miss, perched on top of 100m clifftop overlooking the lake and has all the attributes a castle should==towers, ramparts, terrace, etc. Access to the castle via road is the long way round and for those who can walk the best bet is to take the path number 1 labeled Grad (Castle) from behind the church and climb up the switchback path to the top. It's quite strenuous, but the views alone are worth it.
After paying your 600SIT entrance fee you can collapse in a cafe on the terrace or wander around the museum. There is a large collection of swords, armour, coins, etc from Bled's historic past as well as a small gift shop. There is also a small chapel containing a painting of Henry II and his wife.
The views from the castle are amazing and offer a good view over the whole of the lake as well as further back into the valleys behind. It's best to go up as soon as you have a clear day as in the afternoon the clouds can start to roll in.