These images were generated by sampling Flightradar24 data at two minute intervals over a week, and tracing on a map each plane's trajectory. Red lines are for planes that are dropping altitude, green lines are for planes that are climbing. Where they meet the colors blend into yellow.
Click on any image for the full-size version.
Here are the air corridors around Schiphol airport in Amsterdam:
Here are the air corridors around Paris.
Roissy Charles de Gaulle airport is at the centre of the image. You can clearly see the red approach and green departure corridors. You can also see how the pilots line up with the runway well in advance (yielding long, straight red lines), but they turn away from the runway alignment early in the flight (yielding green lines that curve away right from the airport).
Further south, we can see Orly airport, whose air corridors all seem to point south, which I take it is to avoid interfering with CDG's airspace.
We can see that planes all seem to completely avoid flying over the city of Moscow.
Almost all flights coming to Edinburgh (centre of this image) arrive from the south, and they all trace this big arc around the city to line up towards the south-west for landing (which explains why it seems there's always a sideways plane in the distance in the Edinburgh sky).
There is also what looks like a holding pattern zone south of the city (the roundish blob of red). You can also see Glasgow airport to the west.
All planes leaving Frankfurt towards the south-west turn left at take off, even if only to turn back right a bit further. I guess they're avoiding flying over the city?
Loads happening around London. Heathrow airport is at the centre of the image, at the point where the two bulges of the big red "B" converge west. There are what look like four holding areas, forming a square around the airport.
If you look closely you can also see Stansted, northwest of LHR, Luton, to the north, and Gatwick, to the south. You can tell where they are by the pointy shapes they create in the green lines — flight paths diverging from the end of the runway.
Almost all planes arriving in the Canary Islands it seems come from the north, and they all do a tight half-circle before landing (why so tight?):
Finally, he are the main air corridors between London, Paris, Amsterdam and Zürich:
You can have a look at the source code of the script that generated these pics. It relies heavily on my collection of miscellaneous general-purpose Python utils.
contrailz.com has similar images, with world-wide coverage.