In Dolmen, there is a Trophy/Achievement called The Secret Grove, which asks you to find — you guessed it — the Secret Grove. Like the Vahani Archaeology Trophy, this one requires you to enter a hidden location.
This one takes place in Act 2 of Dolmen, near the arena where you fight the Ferronightmare.
Here’s a video that shows the exact path you’ll need to take:
Your starting point is the Power Plant teleporter in the Wastelands.
All you have to do to pop the Trophy/Achievement is enter this little cave area. Once you set foot inside, you should have earned it.
In that same room, an alien named Nicole will give you a Driller Flame Tank, which you’ll need in order to construct the Driller Pickaxe. Another alien named Rafael will give you a set of Tretaxe Parts.
And that’s really everything you need to know about finding the Secret Grove in Dolmen!