Location: Low Tatras, Slovakia, elevation: 1800 m. Can anybody identify this plant from Slovakia mountains?
I think this is some kind of Hypericum. In Costa Rica and the Andes there is a high altitude ecosystem called the paramo in which shrubby Hypericum are characteristic species. The area in your photo looks to be covered with shrubby species, and you are at decent altittude. Looking at your picture (at full size) the leaves look approximately decussate which is typical of the genus, and also, the stems are ridged which is also pretty characteristic.
There is a good paper here on Hypericum of the Mediterranean region. It mentions some groups that are shrubby or dwarf but thus far I have not been able to find a species that looks just like your picture.
Update: Possibly it is Hypericum aegypticum which looks about right relative to your picture, esp, the leaf color and size. Also known to grow at that altitude. Decent picture here plus the one at Wikipedia both look similar to yours.
Update 2: On fresh look, the bases of the leaves for Hypericum aegypticum don't compare well to your picture, but I still think it is a Hypericum.