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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Fencer: I've seen that one before but I'd forgotten it.
The 30 days value is about 4100. It doesn't seem to discount the non-countable one-peekers, though, so I'd say my estimate is more accurate as an active players count whereas the languages page (and the raw players list) is a logins count.
(verstecken) Hast du lust auf ein schnelles Spiel welches sicher in den nächsten zwei Stunden beendet ist? Starte ein neues Spiel mit den Zeiteinstellungen 0 Tage / 1 Stunde, Bonus 0 Tage / 0 Stunden und Limit 0 Tage / 1 Stunde. (TeamBundy) (zeige alle Tips)