Smallest International airport I've flown in/out of was Harare in the late '80's. There was no terminal as such, but a double width garage that you walked in one end, handed over ticket, then took your bags out the other end to the tarmac under the plane you were leaving on. Bear in mind this was in apartheid days in South Africa, so to fly SA to Australia you had to fly Air Zimbabwe out of Jo'burg, into Harare, then swap to a Qantas airbus plane coded as Air Zimbabwe.

Smallest airport domestic was between BNE and Mt Isa in queensland, can't recall the name. This was before jet service or more than single prop, so if you were flying into wind invariably you would need to drop into this airport to refuel in order to make it to Mt Isa.

Another small but fascinating airport is Longreach in Queensland, the home of qantas. Again a refuel stop en route to Mt Isa, with the advantage of the Qantas museum there where you'd wander round whilst the plane was refuelled from drums of fuel. The guy at the airport was the control tower, radio operator, mechanic, fueller, museum attendant, sheep farmer etc.

On those single prop planes the inflight meal was a box of sandwiches, and a case of cans of pop which the two passengers last on had to have on their laps and pass around during the flight. Don't ask about the toilets, other than you couldn't pee more than a coke can at a time and not be shy. Never saw any female pax on those flights