If you have completed Watch tower quest you will have access to the cave at center of Gu'Tanoth (Just south of Yanille and North of Feldip hills). The area contains a cage of many Greater demons, several Chieftain Ogre, and 6 Blue Dragons. Not many players are there and you can have more than 1 blue dragon.
There are many spots where you can train as mage or archer without being harmed. So if you want to gather dragons' bones, blue dragon hides, half keys, or clue scrolls, Gu'Tanoth Cave is a perfect place for you.
