As I use my D810 and D500 for aviation I decided I can live without my D750. Likewise the 200-500 lens. I don't want to part with either but, as 'they' say Needs Must. That said, my D750's most recent and final outing was to Düsseldorf at the end of March.
Mentioning Düsseldorf, it's easy to do in a day from the UK (sadly not from Southampton, I had to go via Manchester) and has a cracking viewing terrace which, although you have to access via a security checkpoint, you can take liquids onto. Even better is the airport bus tour, which is a bargain at €12.50 each, as you get views like those above.
A couple of views from the terrace: