I seriously don't know how and couldn't find a guide on it.

Explore > Darkside > little blue place on the right It only stocks one item at a time a few times a day. These items cost wizard tokens. c: Do you need to know anything else about it?

Oh so I DON'T need to go on a quest to gain access to it like I did with the blue building then? Because I thought I did. Thanks for letting me know. :P

Nope, it's just a regular place that anyone can enter! I forgot to mention that if you refresh too often (more than 2-3x per hour) you get kicked out and can't see items for a while.

Thank you~! I was really confused but I understand now.

No problem. C: Good luck! Don't get discouraged if you don't find anything for a while. Sometimes I go for months without even seeing anything in there. c:

I have NEVER seen anything in there...haha.