It seems, following the recent post about the railway station terrace at Dusseldorf Airport being closed, that this is now open again and may have only been a temporary thing. Work is indeed underway in the building, so it may be that closures will happen again sporadically. A recent report states that the cafe downstairs has gone, and that access to the terrace is only by the lift now.
Airport Spotting Guides Europe Book
The new book by the author of this blog covers 35 of Europe's best airports for spotting.
Each guide includes a map, spotting locations, technical information, contact details, list of airlines, list of aircraft stored/preserved/wrecked at each airport, and details of the best hotels and rooms to stay in.