What I miss most in gymnastic is the daily training and all the competitions I had.  The training was really hard, really intensive and I liked to surpass myself by doing incredible things.  Now it's impossible for me to go on a beam and try to do my highest jump ever or just go to the bars and try to fly as a bird.
I also miss doing competitions because a championship is, for a gymnast, the result of your training. The atmosphere is so strong and you can see what the other gymnasts are able to do.  A competition is constructive and rewarding because you see what you are able to do under pressure and you learn about the other gymnast.

And after a competition, you just want train harder than ever...