Lemnis Gate

Let's get this party started!
Find the secret robot party in the tutorial

Both written guides are accurate in explaining what you have to do. I just want to share a video guide for anyone struggling to get this achievement.

To unlock this achievement you have to start the time loop tutorial (it's the tutorial right after basic training). Follow the games instructions until you are allowed to choose an operative. Select Karl (other can reach the starting area as well but the achievement won't pop unless you are playing as Karl) and turn around then head towards the vent that you came out from as a drone. You have to be quick as you only have 25 seconds to do this. Now follow the vent back to the starting area and once you haven't exited the vent lights will begin to flash and the robots that were broken on the ground will start to dance. Your achievement will pop then

This achievement can be earned during the Time Loop Simulation portion of the tutorial. When given the opportunity, choose karl (while toxin can also get to the secret area, karl is the only one capable of earning the achievement, it is a robot party after all), immediately turn around and re-enter the vent you first came through with your drone, follow the vent all the way back in the 25 seconds allotted and you will find 3 training bots dancing in the starting room for your achievement.