Berlin Botanical Garden
This is the most beautiful botanical garden that I have ever seen in my life... It is located in Berlin, and I really recommend this place for a visit. You can see thousands of plant species, those from tropical rainforests too.
Also, there is a museum which shows the history of plants and their uses with very nice pictures, sculptures... Do not miss it out! Get ready to spend a whole day over there and get some drinks and food with you, or you can sit in their cafeteria if you prefer.