There are flights to Abha from [wiki=a2579de70254b8fbc9116eb8a259e612]Medina[/wiki], [wiki=1abf78bf4a6d3cbfff7a0b66a203c755]Riyadh[/wiki] and [wiki=e45c2028046d99deab4fd1c38baa989b]Jeddah[/wiki].
The drive to Abha from [wiki=66c1aad0f04865a022f0e7132d93abc9]Khamis Mushayt[/wiki] can be very interesting trip, but as usual drive carefully. The road from [wiki=58ef507056f88130290f4cb6ca3ec7dd]Sharourah[/wiki] via [wiki=53a4c458cc946d9b1b336367b44244bc]Najran[/wiki] is daunting, but interesting - up and down ribbon across the dunes, with an old version off to one side for may kms. There were Camel warning signs along it, but some were single hump silhouettes, others had 2 humps !
You can also drive in from the west coast , with lots of winding roads, bypassing old washed out bridges, lots of signs of floods, some picturesque villages etc, or from the north from [wiki=40f245f002555c4a6105d6066d2bdb85]Taif[/wiki] - lots more twisty roads, and not as interesting as going to the coast. Neither trip offers much in the way of accommodations, so be prepared to camp out.