In former Czechoslovakia, it was popular to grow lemons from seeds indoor. It took many years to fruit, but seedlings were adapted to indoor conditions and short days during winters.
Years ago, there was a spot in TV news about one fruiting gapefruit seedling in pot in the Hrebienok ground funicular station right next to the ticket Office. Hrebienok is 1285 meters above sea level. The tree is there for more than 30 years.
Some pictures from that show:
Picture from 2012.
Grapefruit is now under name "Popradsky" expanded in collections.