Visited 20th September 2003: We visited the barrow on a circular walk, but if you wanted to see it for its own sake access is reasonably good. The nearest road is only half a mile away, and the barrow itself is on a public footpath.
Round barrows are quite unusual in this area (round cairns are much more common), but Gelli is one of a small selection that have survived. There's a relatively modern hedge bank (minus the hedge) running through the barrow, so from some angles it looks very wrong. The lack of cultivation in the area means that the barrow mound is still quite large, but I have no recollection of seeing a surrounding of ditch.
Not a spectacular site, but a nice enough place to visit if you're based in the area. The gradient from the road to the barrow is relatively shallow, but the path isn't good enough to get a wheelchair up without some difficulty.
As an aside, I only realised after our visit that Gelli is visible against the skyline from Banc Bwa-Drain, so now I get to see it on a regular basis (as a tiny lump in the distance).