Blyde Lake is not big, there is a castle around. The best way to explore Lake Bled is to walk around the lake on foot. When you are around the lake, there is a best viewing angle on the mountain (must remember to go, won't let you down!) At the top of the mountain, you can overlook The whole of Bled Lake and the small island in the lake, this should be the amazing scenery that I have seen in the past six months.
Suggested play time: 4-5 hours, if you have time to stay in Bled for one night is also a good choice.