Hi Singy from that smart fine city: have to disappoint a lot: there simply are NO trains at all running anymore overnite in ESpana, so superfluous. Perhaps you read an old guidebook.

THere are just a very few overntie trains in EUR at all, most are INTernational and offer both seats and sleppers/couchette (read seat61com for the difference-its quite other as f.e. used to on KTMB from JB) and all need you to also make a RES with pass and pay extra for it. Many claim that such a trip replaces a HOtel-I´ve found that to be just partly true: a hoStelbed, so often used by young travellers, tends to cost less as that and offer way more in comfort. Using a normal seat is comparable to in an airplane. In general these overnite trains-revived a bit the last yrs, are rather overhyped.

Even more warning; ESpana has trains by RENFE and its a big PITA to make the RES for them-about all need, the network is not that dense and its simply the very worst country in being nice to passholders. IF you mainly/only ant to travel there (such a long time?) then very much look into other ways too. It also has an extensive network of long-dist buses (coach for Brits) and these are also overnite. There is also a special Spain Railpass from RENFE with which you can RES online included. lah!

Thank you for your response! Appreciate it :)