This is the 12095th most frequent Polish word.
lotniskiem
"Lotniskiem" means "airport" in the instrumental case in Polish.
The word 'lotnisku' is the instrumental case of 'lotnisko', used here to indicate the location of the meeting.
Spotkaliśmy się na lotnisku, aby pożegnać podróżnych.
We met at the airport to bid farewell to the travelers.
'Lotnisku' in this sentence is also in the instrumental case, describing where the services were provided.
Podróżni byli zadowoleni z usług oferowanych na lotnisku.
The travelers were satisfied with the services offered at the airport.
Here, 'lotnisko' is used in the accusative case, as it indicates the direct object of the verb 'poprzez' (passed through).