Lago Caballococha (LHC / SPBC), Peru, on a seaplane from Iquitos operated by the Peruvian Navy. The service apparently no longer exists. There is an asphalt runway now; but back then you landed at the mouth of the lake and motored over to town. The "airport" at LHC was just a fishing boat dock. The old (water) "runway" is at left.

You paid for baggage by the kilo, and people bigger than about 150 pounds paid a supplement. The pilots were great. Ground services, provided by a few conscripts, left a little bit to be desired. It cost like $10. Then there are the missionary air services, if you want to get really remote...

In a different place altogether, I was at ADK (Adak, Alaska) a few months ago... big infrastructure (former Navy Base); but only two flights per week, both 734 Combis from ANC, with an average of about 20 pax each. About 150 people on the island, and it's 600 miles from the nearest "big" town, Dutch Harbor. That's gotta count for something. Must be the most remote / smallest (in pax numbers) airport in the US with 737 service.

Heading back south:

Providencia, Colombia (PVA). The airport is just an open pavillion, with a bathroom and one or two small rooms for the administration. They had a couple of Twin Otters a day from San Andres (ADZ). Then they lost one. Then they had Let-410s, I think, for a while. Lost one of those too. I don't know what they have now.

Tulcan, Ecuador (TUA). Used to have 737-100s from Quito a few times a week, operated by the Ecuadorian Air Force. 20 minute flight, like $15. Until one smacked into a mountain. Knew somebody on that flight.

And Bahia Solano, Colombia (BSC). Basically the same deal as Providencia. The "terminal" is a slab of concrete covered by a roof. They had Twin Otters operated by Aces, now defunct, until they lost one (knew somebody on that flight too). I went on a Dornier operated by Satena, the Colombian Air Force's airline, that went Cali (CLO) - BSC - Nuqui and back. We were the only 2 pax that day from BSC to CLO, and they told us they were not going to land the plane just for us. We complained so bitterly that the airport manager radioed Nuqui and had them reinstate the stop just to get us out of his hair. :-)