Your first thought will be probably "Why is she even putting it here?!" After going there, it will probably change into "God, I got her point now". The National Library of Technology is situated in the students quarter Dejvice and You can take a walk here from the Castle. The building itself is magificent and even more phenomenal from the inside.
No matter how much into technology You are, this is a must see! You can get in without any problem, so just take a look. The whole interior has lots of technical jokes to offer and even some "normal" books in the shelves. If You are looking for a place to chill or study, or just want to use free wi-fi, this is the right place to be.
Go to the last floor and check out the view,)