ok thanks .. i missed that

Rudi,
it's next to the Slave Cells where you rescue Lady Almalphia, Its the same room where you fight the Berserker, Veteran, Highwaymen and a couple orcs.
There's a table in the corner with a chest by it and a button on the wall to open the Secret Door out of the module.

Great module. Really enjoying it. Where is the exit?

Yes, its a full campaign, but it starts with Haunted Keep of the Slavers. Go to Collections and see the Slave Lords Campaign entry. Then you just click the Subscribe ALL button at the bottom,
The Instuctions are here... for general knowledge
https://steamhost.cn/steamcommunity_com/app/1096530/discussions/0/3041605810444698965/

Here's the Full Campaign...
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2567260607

It starts with Haunted Keep of the Slavers.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2544471368

Is this a new campaign that I can play with Solasta? And if so how do I download it and make it work?

Glad you liked it Triple.
Oh by the way, since I know you from the Solasta Forums, I am almost done with the 3rd one which is Stockade of the Slave Lords. If you're interested, I would possibly have you take an early run through of it once I'm completed before I release it to see how it plays.

Tremendous Module and it was great to experience the new environments from the Sorceror Update.