Retrieve the battle plans from the hideout under the broken highway

How do you complete "Retrieve the battle plans from the hideout under the broken highway"?

This is step 2 of 3 in Echoes of Victory Ridge, given by Celeste. It is completed on Dam Battlegrounds. The exact location is marked on the Dam Battlegrounds map.

• Echoes of Victory Ridge
• Dam Battlegrounds

What are the other objectives in Echoes of Victory Ridge?

Echoes of Victory Ridge has 3 objectives in total: Reach Victory Ridge, Retrieve the battle plans from the hideout under the broken highway and Deliver Major Aiva's Patch to Celeste.