Spain, outside of the lines connecting Vigo, Barcelona, Madrid, Malaga, axis.
Greece, anything outside Athens - Thessaloniki.
For example, the Shinkansen in Japan (which I totally recommend!) is usually over $100 USD. Which is pretty similar to a flight price. This pattern repeats in Europe as well.
My friend just traveled London -> Edinburgh in the last few weeks, and found the train 2x the cost compared to RyanAir or EasyJet.
Even in the US, this pattern holds. Seattle -> LA costs $50-150 by plane, depending on the airline (3hrs). By train, it's 35hrs and $150. Its a lovely train ride, if you have a weekend to dedicate.
I went by train to Germany during the autumn of last year and oh man, what a pleasure it was. I got there about 5 minutes before the train, got in, dumped my suitcase and had room to spare.
During the trip I sauntered between carriages, bought some (mediocre) food to scoff down in the restaurant carriage, which I opted to do at my seat rather than right there because I felt like some quiet time rather than the buzz.
Later I traveled by plane to Spain in the spring and as nice as Barcelona was, I couldn't say the same about the plane trip, which was a necessity rather than a pleasure.