Heathrow Airport didn't open with a railway connection. The Underground (metro) was extended to the airport in 1975-1977. The first heavy rail connection open

Heathrow Airport didn't open with a railway connection. The Underground (metro) was extended to the airport in 1975-1977. The first heavy rail connection opened in 1998. A significant extension to this connection (trains right through London) should open in 2023. There are also buses, which can be useful for the nearby suburbs, but are probably used more by staff than passengers. (The one time I used one of the local buses, it stopped at the freight terminal, then a staff-only entrance, then the passenger terminals.) Most medium or large airports in Europe have a rail connection to the nearest city. Smaller ones have express buses to the city centre; at the smallest ones the buses are only scheduled at flight arrival/departure times.