I love all cycling (and am glad I'm not alone in this thread!), but long-distance cycling (called audax) is my thing that other people think I'm nuts for enjoying.
"Long" starts at 125 miles (200km) and upwards from there; I do one 200km+ ride once a month, and have done for eight years. I just love it. Seeing the change in the rhythm of the seasons; seeing the swallows arrive, bidding them farewell. Sometimes with friends, sometimes solo, sometimes a bit of both. I quite often get out for a 200km ride on my own on New Year's Day; seeing the first sunrise and the first sunset really sets me up for the year. Plus the roads are really quiet, and everyone who's out for a walk is cheery - I spend all day wishing strangers a happy new year, which is a great start to the year. (my kids are all teens and young adults now - by the time New Years day rolls around, they and my husband are all totally sick of the previous week of me bouncing up and down trying to get everyone out for a walk, and are very happy that I go off on my own for the day while they slump in front of the tv with the quality street)
The UK is such an astonishingly beautiful country - it's so varied, and 200km is a perfect distance to see huge changes in the landscape. I particularly love looking at churches as I ride. Not the inside particularly - that's usually much the same - but the outside. The building materials used to make churches so often reflects what's under the ground in that locality - it's like they have grown up out of the ground. I love UK landscapes so much, and on my bike I can eat it all up.
Oops that was an essay, sorry!