The best reason to visit Berlin for a weekend end of August is to attend the Long Night of Museums on the 25th. With hundreds of museums to choose from, it will be hard to prioritize which one first. If I were in your place I would go to some hidden unknown gems of contemporary art and photography, as the others, those on museums island, will be so crowded.
Here is a flight just for the weekend, more dates available if you search on momondo. Accommodation will be an issue as it is usually very expensive, so start searching for right away. Check my other posts about Berlin don’ts and some tips. Summer in Berlin is another kind of experience, more outdoors, more hipster kind. Personally I love it though not many would enjoy to smell weed on terraces.
Note that we are not an online tourism agent and do not provide services of any commercial type. We just share what we find and give you suggestions about great destinations in the best periods. Just follow the link to book by yourself.