I’m always amazed by people that can do long rides inside.
I had an interesting experience this year where I got a little flat in May and then had to ride a 600k and 1000k in June. I decided to ride a couple of 100km a week, and that really seemed to help. That has always been a key training distance for me. Like I posted up-thread, anything up to 300k seems to have a positive training effect, but with 100km rides I need a lot less recovery.
Unfortunately, I blew up my legs in July with back-to-back 200km rides in very hot weather. I had horrible cramping the first day and the heat was so bad the second day I was incredibly slow. I really had a hard time recovering from that.