are at least to my experience one of the best investments when it comes to real estate investments.
If you can afford a block instaed of a single or a portfolio of flat, go for the block.
In my post “Why you should not buy a flat” you can read why.
The income is spread among a couple of renters and the income is very stable, in most (if not all) Berlin areas even growing. In the right areas growing fast (2012).