These seem to be (to have already) disappearing(ed). I took overnight trains while in the Army in the mid 1980s and again on my honeymoon in '96. Now I want to share this excellent experience with our kids, but high-speed rail (yay, usually) seems to be killing overnight train travel.
Spain is not on our itinerary, but Italy could be. Athens is our departure city back to US.
Any suggested routes?
Correct, there are no more night trains from Paris to any international destination other than Italy and those within France are also very minimal, with weekend (only) service to Hendaye ending about June 30 and Nice service expected to end in October.
The Paris-Italy night trains operated by Thello are not fancy and not always well reviewed by travelers. I'd say the same about night trains within Italy. A couple of more popular routes for travelers are Munich-Venice or Vienna-Venice. See a partial list in the PDF version of our Rail Guide. The Man in Seat 61 is also a fan of night trains and has info by route.
It's not just high-speed trains, but also budget airlines, that have killed off traditional overnight services.
Paris isn't completely without night trains! Don't forget there is still the Moscow <=> Paris night train, which also serves Berlin and Warsaw. Unfortunately, this year it only runs once per week, departing Paris on Fridays.
