The journey to the airport as you prepare to depart a country you've been discovering is an extremely strange one.
On arrival, as you make the leap from airport to accommodation, it is all excitement. Everything you see out the window is something that you can get closer to in the coming days. The exploration is all ahead of you. But when leaving, everything you see is something that you will now not have the chance to explore until a return visit. In all reality, something you will never experience.
Sadness is always a part of departure, be it leaving home for the beginning of an adventure or saying farewell to a country you have only just scratched the surface of. No single trip could ever contain all you need to immerse yourself in a culture.
And so as you leave, there are small shops outside the window that you would have loved to visit, restaurants you had not spotted the day before, interesting characters lurking on a street corner, a street market hidden between two panicked, weather-beaten buildings that you feel sure would house the best coffee in the city.
All of these things fly past your window, unable to be visited, nothing more than a fleeting image you may never get the chance to expand on.
Such is the joy of travel. It can never be completed. No one has every seen everything. It is impossible. Definitely worth a try, but in the end quite impossible.
This final journey is usually the time my brain recalls all of the times I said no on the trip. This is particularly rude on the part of the brain because it waits until the moment nothing can be done to correct it.
You can't take back your decision to sleep in last Thursday, you can't even take back the ludicrous decision you made at breakfast concerning pineapple. It is all done. Soon you will be in a plane watching the city slowly disappear behind a towering, cloud peaked mountain.
Or fading into a steady drizzle if it's London.
My most recent case of this frustrating frustration came while sitting at Newark Airport, in the midst of being comprehensively beaten at Scrabble.
I don't think I am revealing anything too shocking here, but there are a lot of cities. Heaps of them. They are all over the place. And not too many cities have the expectation and grandeur of New York. Everyone has heard of the place and most have taken a moment or two imagining walking the streets.
At the age of 31, I finally spent a week in New York. It was sensational.
We walked the streets and made references to our favourite television shows growing up, listened for the many, varied accents and recreated them as we fell asleep each night, respectfully obeyed the two drink minimum at a comedy club and consumed food cooked in a truck while lining up for a Broadway show.
I was exhausted. We had done what we could of New York.
But there was something I didn't do. Actually there were so many things I didn't do. I didn't get the street hotdog I so craved, I didn't get my haircut by an ageing man with a thick accent and a shaky hand and I didn't come close to working out how to tip correctly.
All of these things I can shrug off without difficulty. But there is one thing I can't quite forgive myself for.
For months leading up to the trip, my plan was to go for a run in Central Park.
Now, we did set a blisteringly good time riding around it one sunny Wednesday afternoon, and it was one of the great days. A day that will stay somewhere inside forever, popping out occasionally when a smile is needed
But I had said I would run.
Each morning I would wake up exhausted from the previous days energies. Despite considering ourselves quite the experts on the subway (let's not go into the story of when I departed a train without reminding my girlfriend it was our stop, only to then see her waving from behind the recently closed doors), we spent most of our days walking.
I have recently realised that I be becoming an old man slightly early, and the stiffness I felt in my legs each morning of New York is one of the things that tipped me off. There was also the incident during which I conceded I simply must increase the text size on my internet browser permanently.
'I'll do it tomorrow' became a regular chant within Room 1017 during the morning hours.
But not once did my running shoes meet the Central Park surface. And it is the one decision from that trip I can't quite let go of. Really it all came down to desire and I let myself down.
In my old age, I am beginning to find a much better way of dealing with this.
I still sulk about it for a fair length of time, there is no doubt about that. But at some stage it becomes motivation for the days ahead, regardless of the setting. Try not to feel the same regret about something else.
There really are a whole bunch of cities. And we can't do everything we want in all of them. But we can try.