Outside Grate

YOU ARE IN A 20-FOOT DEPRESSION FLOORED WITH BARE DIRT. SET INTO THE DIRT IS A STRONG STEEL GRATE MOUNTED IN CONCRETE. A DRY STREAMBED LEADS INTO THE DEPRESSION. THE GRATE IS LOCKED.

From here:

You can go back to the forest forest. Or you can go back to the stream in the valley. Or back to the beginning of the road. Or, if you unlock the grate, you can go below the grate.