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.
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dmk: That is correct. Once you at the top (or even on the bottom), you do not have to challenge anyone - so in a way, you can protect your spot until someone climbs up to you to challenge you.
(hide) In the mood for a quick game that is guaranteed to finish within 2 hours? Create a new game of your preference, select the Time for game and set Time to 0 days / 1 hour, Bonus to 0 days / 0 hours and Limit to 0 days / 1 hours. (TeamBundy) (show all tips)