Right, it's DONE 💪

Every railway border between
All 🇪🇺 countries
🇳🇴
🇨🇭
🇬🇧
🇱🇮
🇸🇲
🇻🇦
🇺🇦
🇲🇩
🇷🇸
🇧🇦
🇲🇰
🇽🇰
🇦🇱
🇲🇪
now mapped...

Inc. existing lines with passenger trains, lines without passenger trains, and derelict lines too. Even tramways and narrow gauge are mapped

Here's the Zoom-able version
https://umap.openstreetmap.fr/en/map/crossborderrail-all-the-borders_838780#5/52.999/7.747

Now tell me what I am missing, and where I ought to go next 😊

Grey icons are the places I have not been!

#CrossBorderRail All The Borders - uMap

@jon You wrote three times "No idea what this was" between LV and LT. That were german military railways built under WW I. According to Hesselink's book "Eisenbahnbahnen im Baltikum" threr were five that crossed the current border. More comes.
@heisebahn These three appear in the European Commission's 2018 report on cross border railways, but no information is provided about any of them. Searching online did not dig up much!
@jon No wonder. Many of these lines existed only during the war and are poorly documented.
There could only literature about the "Heeresfeldbahnen" help, maybe. I have one book about them and am quite sure where to find it.

@jon The book https://d-nb.info/954658167 has no further information.

For the latvian line to Nereta the 1924 timetable (russian) is available at https://parovoz.com/schedules/latvia1924/latvia14.php. The lines there have an article in latvian Wikipedia: https://lv.wikipedia.org/wiki/Vies%C4%ABtes_%C5%A1aurslie%C5%BEu_dzelzce%C4%BC%C5%A1

DNB, Katalog der Deutschen Nationalbibliothek