Infiltration

Walkthrough
The Dragonborn meets Stalleo, sitting by a campfire along with his small band of mercenaries just outside of Treva's Watch, to the east. Stalleo explains that while he and his band were away fighting the war, his keep (Treva's Watch) was overrun by invaders who also kidnapped his family. He asks the Dragonborn to help him enter the watch by using a nearby tunnel, Treva's Watch Escape Tunnel, to enter the fortress and find the lever inside the courtyards to open the front gate for him.

Use the backdoor to gain access to Treva's Watch
Enter the Treva's Watch Escape Tunnel and keep following it until reaching the castle yard, taking out the bandits that get in the way.

Use the lever to open the gate to Treva's Watch
Once exiting into the yard, the switch to open the main gate is right in front of the Dragonborn. Activate it to open the main gate.

Meet up with Stalleo in the courtyard
Stalleo and his guards enter the castle yard, meet up with them.

At this point the Dragonborn may already have taken out all the bandits in the castle, and will receive his reward. If not... some clean-up may be required.

Bugs

 * The quest stages are shown but never check marked as completed, the whole quest can be completed though.

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