It is window with tools such as magic-wand -selector but cannot find anything from Tools or View -dropdowns. So how can I get the Tools -window back after closing it?
"New Toolbox" in Windows -dropdown like below and then you will get it. I thank Bill for helping me with this in Freenode, have Fun!
In addition to your own answer: if you are in Single-Window-Mode, then just press the Tab key on your keyboard.