@siegeavecvue you're proposing the "how far can you go with a four day interrail pass", let me propose this two travel day marathon (for lack of a better word)
Warszawa - Cadiz in two travel days
Warszawa
Wroclaw
Leipzig
Frankfurt
Paris (Intercité de Nuit from here)
Toulouse
Narbonne
Barcelona
Madrid
Cadiz
https://www.sbb.ch/de?stops=Warszawa+Centralna_I5103360~Barcelona+Sants_I7171801&day=2026-02-04&time=06_15&moment=dep&trip=1
https://www.sbb.ch/de?stops=Barcelona+Sants_I7171801~Cadiz_I7151405&day=2026-02-05&time=12_21&moment=dep&trip=0
https://signal.eu.org/osm/#locs=52.233374,21.071149;51.346552,12.383086;48.877098,2.359491;45.835424,1.264485;43.604464,1.444243;36.529744,-6.292898
4'200 km in 39 h, surprisingly only four countries
Only one problem: #DB is involved