A good round of some nice hills!
Assuming you went up Y Garn first and descended after Elidir? If so, there is a path more or less on the line of your descent route - a narrow trod, not easy to spot, but it weaves its way easily through some fine scenery including the Mushroom Garden. There are the remains of a molybdenum mine there.
If you are around that area again, it's worth going on to Carnedd Y Filiast, if only for the sight of the bizarre Atlantic Slab with its regular "ripples" and quartz veins - similar in angle and scale to the Beinn Trilleachan slabs, but seemingly less well known.
Tim