Lake Bled and the surrounding area is beautiful! And there are various activities that you can participate in while in the area. Let's start with taking a good walk around the lake. There is a well developed foot path that will take you the whole length of the lake. The distance is 6 km (3.3 miles) and it should take about an hour to complete. It's easily do-able.
After getting a good sweat from walking, I would recommend taking a boat to Lake Bled island which is in the middle of the lake. It's a small natural island with a church in the middle of it, I learned that a lot of couples like getting married on the island and the groom has to carry the bride up the steps leading to the church (I counted 100 steps but Tanja counted 98).
Inside the church there is a rope that you can pull to ring a bell, it's believed that if you make a wish and ring the bell then your wish will come true. No harm in giving it a try. The boat ride to and from the island costs 15 euros/person. You can also rent a paddle boat to get to and from the island by yourself.
Once you leave the island, you can visit one of the souvenior shops in the area or stop by a cafe to enjoy the famous Bled cream cake. It's light and tasty if you enjoy pastries, you can even have it with a desert wine like moscato. They actually offer that combination and if you don't want to drink you can have the cake by itself.
After getting those calories in from indulging in the cream cake, you can make your way to Lake Bled castle which sits on a high cliff overlooking the lake and surrounding area. There is nothing fancy about the castle but the view you get is worth a visit. I almost forgot to mention that you can also swim in certain designated areas of the lake.
That's it folks! However you decide to spend your time in Bled, it's definitely worth a visit.