Haugen Tower is in the middle of the route that leads from Cardali City to Genradex Town. Haugen Tower is a battle tower. Most the people who enter to battle others have there pokemon leveled up to almost fifty. If your pokemon are not at least forty five you have no hope of winning.
To enter you must solve three riddles from the guard at the gates. Once you have solved those three riddles you will be sent on a quest for something. Than and only than you may enter Haugen Tower.