There’s the Trans-Siberian Railway, Beijing to Moscow, takes seven days I think. I knew a guy who rode that. Sounded uncomfortable, but he enjoyed it.
For true luxury, there’s the Eastern & Oriental Express between Bangkok and Singapore. (Actually, I think it goes as far north as Chiang Mai.) Too rich for my blood. And I don’t even know if it’s running anymore, as Covid has shut down a lot of Southeast Asia.