Smallest airport for me is HKK... I believe only B1900's operate in/out of there (possibly Jetstream 32's in the past as well?)
It DOES have a small terminal building with a cafe... so not TOO small!
OTOH the smallest "landing field" for me was HMAS Sydney... an FFG with a flight deck.. operating an AS350B and an S70-B-2 in my day.... the Seahawk made the deck look..... very small!