To find out what stairs you can currently challenge someone in, first go to the Main Stairs Page, then click on "Show your stairs only" link. The ones in BOLD are ones you can make a challenge in. .
Pioneer54: Regarding that 20,000 players value: Go to the Players list and sort it by Last action so that today's action is shown. Then go to about page 85. That shows the players whose last action was about a month ago. There are 50 players shown per page so thats about 4250 players in the last month.
If you examine that page you'll see that there are a lot of Pawns who joined, had a look around and haven't been back since. The number of those decreases as you come further towards the present day. I counted 20 on page 85, 30 on the previous page, 35, 34, 33 on previous pages. On page 70 it was down to 20 non-countables, page 60 had 13... So let's say about 600 players in all. There are those who were active more than a month ago but who will be back sometime, but probably much fewer than the one-peekers. That's then roughly 3700 active players.
(do skréše) Chce se tě zrovna valet rechlé špil, keré zaročeně skonči v pruběho dvó hodin? Vetvoř nabidko ke špilo a zadé tam Čas na špil: 0 dni 1 hodina, Extrovnica: 0 dni 0 hodin, Limit: 0 dni 1 hodina. (TeamBundy) (okázat šecke vechetávke)