Pretty easy achievement, all you need to do is travel to the 'Guild Stronghold' from the travel gate menu. Obviously you need to be in a guild to do this, if you aren't in one there are a few forums on TA about guilds you can join or just PM me and I can get someone to invite you to the Guild I'm in.
Hope this helps!
Note: The guild I am in is full so you will have to message another guild leader and hope they let you join. Sorry for inconvenience.