Not really - the only trains taking longer than 24 hours in Europe are the sleepers to Moscow, and the longest of those (Nice-Moscow) only takes 48 hours. There are then much longer trains from Moscow into Asia though, up to the famous Trans-Siberian (6 days).

I went London-Japan overland but my longest single segment was two and a half days (Moscow-Shymkent), and that was about right - time to relax and do nothing for a bit, but by the third morning I had definitely spent enough time in the same compartment, as nice as it was.