The tower arena is a progressive content that you climb for rewards. You will find it through the Waypoint, as the image indicates. Once inside just head north and you will find it.
Tower Arena mechanics
The tower arena is divided by floors, the next one being more difficult and more rewarding than the previous one. You can only start the tower arena at anytime as long as you have the entry cost, the Tower Ticket. You can obtain this ticket through Juarez, for loyalty points or as a rare loot from bosses.
Interact with the Tower Arena gate to setup your run. A menu will open, like shown in the image to the left.
As the image shows, you start at floor 1 and you will unlock the next floor by successfully defeating all monster waves from the floor. You will have a total of 40 minutes to complete the floor, otherwise you will be kicked out of the arena.
There is a level requirement for each floor, so make sure you meet the correct requirements before entering.
You can also see the possible rewards in the tower arena menu. If you possess more than one Tower Ticket and wish to improve your loot, you can click on the little triangle near the ticket to consume an extra ticket, up to 5 tickets, which will improve your rewards, but will also increase the monster's difficulty. The tower ticket(s) will only work for the current run, which means that if you get kicked out or die, you will need to use another ticket. The ticket(s) will continue to work if you climb floors within the same session that the ticket(s) was used, so try to climb as many floors!
Dying inside the tower arena will simply teleport you out and no penalties to your level and/or skill will take effect.
Once you finished a floor successfully, you will need to interact with the gate or wait for the time to run out if you wish to proceed to the next floor. The location of the next gate can vary depending on the floor you are. The same menu as above will open once you interact with the gate. You can also choose to leave the tower arena. Your progress will be saved and you will be able to enter again at a later time, if you wish. Leaving the tower or dying before the waves are finished will cut your accumulated rewards in half, so be certain that you want to enter the next floor.
Upon finishing your tower run, you will get tower points which you can use to purchase permanent boosts to your character. The points obtained work differently from the other rewards and are obtained from all of the floors below the one you finished, regardless of where you started. For example, if you started on floor 16 and finished on floor 20, you will get all of the points from floor 1 to 20.
Be aware that some floors may have powerful bosses for you to face, so stay alert.
At the moment you may only be able to go in the Tower Arena solo.