Without a doubt the easiest would be a direct Flixbus: 4h30 journey.

Otherwise you could:

- take a regional train to Faro

- continue to Vila Real by train

- cross the estuary by little ferry

- (be careful of the 1h time difference)

- infrequent bus to Huelva

- train Huelva - Sevilla -> Interrail reservations only possible at the station (or in Germany)

I'll look at timetables later. That would take the whole day for sure.

If you’re not in a rush and would like to get the most out of your pass… you could do:

• R Lagos - Faro 07:47 - 09:34
• R Faro - Vila Real de Santo Antonio 09:55 - 11:02
• Ferry every 30 min (10 min journey + 1h time difference)
• Bus M-303 Ayamonte - Huelva 15:00 - 15:59
• Intercity Huelva - Sevilla Santa Justa 17:50 - 19:14

There would be a 11:10 departure but there’s no margin for delays.

The reservation for the Intercity at 17:50 seems also to be available through happyrail.com, switching the search from ticket to reservations.

However I never used this website before because this option is quite new, so feedback appreciated.