Divine Dimension
After the sect leader and the formation were gone, everything else was easy. Some of the members tried to run away and some just wanted to fight to the death, the team gave whatever they wanted. They killed the people who sought death and they just let the people who wanted to escape without any pursuit.
After they escaped, they gathered some information from the dead soul about how to enter.
Sam was quite surprised by this.
There is an underground river that passes through the area under the city. The Tundra Sect dug a hole and created a lake connecting to this river in their backyard and used a formation from which the water wouldn't be able to enter the city.
The exit is also somewhat similar, but instead of a lake, the underground river was directed even deeper and in the downwards direction to make a waterfall.