For those of us who'd rather NOT use the 'contentious' Cuilcagh boardwalk, the most straightforward route of ascent is from the Bellavally Gap to the south.

A telecomms mast sits high on the subsidiary eminence of Benbeg, and its access road (locked gate) gives a substantial leg-up to the pedestrian. At the end of that road the compound is passed on the right in a groove-like path, and a quick plod up a slope leads to a simple stile on the skyline.
This gives access to Benbeg's somewhat indeterminate summit, but also to the enormous sweep of Cuilcagh's eastern scarp, a glorious feature whose brink is followed all the way round to the summit. This can be a bit of a mucky traverse; there are paths but none of them seem continuous and there's a lot of eroded peat about. The outlook is tremendous though; few Irish hills are as well designed for looking over lowlands from highlands.

The final ascent to the summit is more laundry-friendly and grassy, and the top is crowned by a huge ancient pile of stones (with a trig point).