According to Wikipedia (I know, might not be accurate), it says that Nyingchi Airport (IATA: LZY, ICAO: ZUNZ) in Tibet, China is the hardest to reach. Here's an extract from the article
Known as 'the world's most difficult airport for planes to reach', Nyingchi Airport is situated in the valley of Yarlung Zangbo River in the Southeast of Qinghai-Tibet Plateau, surrounded by over 4000-meter high mountains enveloped by clouds and fogs throughout the year. Planes have to fly through the narrow and winding river valley. The narrowest flight path is less than 4 kilometers from one mountain ridge along the valley to the opposite one. According to meteorological data, there are just 100 days overall that are airworthy in the airport each year.
Air China is the sole carrier operating to this airport. Hoping to find some pictures on this site and Google but to no avail, hoping someone can provide a clearer view of how this airport's approach is like. 4 kilometers of space between each mountain ridge does seem dangerous, imagine a strong wind and you look like you are going to hit the mountains soon. If someone could provide information on which aircraft type(s) are being used by CA to this airport, the runway length and the wind conditions, it is much appreciated. =D
Another airport I can think of is Paro Airport (IATA: PBH, ICAO: VQPR) in Bhutan. Only 8 pilots are certified to land at this airport. Similarly, only Drukair operates to this airport with a pair of Airbus A319s. Planes have to climb / descent very steeply to avoid the mountains when taking off or landing in either way. With a single runway of 1985m, it leaves little room for error here.
Therefore, which airport do you think is the hardest to reach in the world and why? (Commercial Airports only please!!)