I used to do this a lot a few years ago.
I stayed twice over night in Transit in LHR
, I guess Terminal 3 both times. I flew Paris-LHR
, stayed there overnight, and LHR
the next morning. All with BA
. The other time I used BA FRA
and then LO LHR
. I was very lucky that back then I had not to change terminals. There were some lounging chairs around, and it was great to wander at night through deserted Heathrow airside...There were some other people too. I slept in the children playground, there was a matress plane I could sleep on. Never slept that well in an airport.
Also stayed overnight in Transit in VIE
. Arrived FRA
in the evening, continued next morning with SkyEurope VIE
. This was ok too, although very few places airside to sleep. Found a single bench which was fine, although it was metal.
Stayed at ORY
, too. At the South Terminal landside you may go up the stairs where the huge windows overlooking the apron are located. on the left side there are comfy turquoise and brown seats. Usually they have a non moveable armrest, but some very few don't and then it's sleeping like on a matress. But it's landside and therefore not that safe.
Then I stayed at ESB
. Landside this time. Airside would have been great as the airport is very modern and they have great benches with no armrests and it's quiet. Landside was fine too, there was a bar upstairs. I took a whole bench for myself and slept like a baby. Was awaken the next morning by the owner, but no problem...
Also spent the night in TLV
landside. This was so so. It was on a floor between departure an arrival where rental cars are located. Benches not comfy and annoying announcements all the time. That said, nobody bothered and I was fine. Continued to sleep airside, once checked in and my flight heavily delayed. This was better, could even sleep on the floor...
Probably the worst airport I spent a night was BGY
. This airport is annoying. A lot of other people around (being typical backpackers paradise). At midnight security people came and told everyone to leave the terminal as they would close it. The put everyone in a amall barrack in front of the actual terminal, which is mostly used by charter flights. It's rather a tent. There put a guard behind a desk, a little bit like in class. Very unusual and defnitely not a nice place.