Here is where you can vist your Houses Common Room or if you are a Teacher the Teachers Lounge. And of course if you are a Prefect then the Prefect's Bathroom. But I am sorry, all of these rooms are password protected and can not be entered unless you have the correct password. Passwords can be gotten from the Head of your House or your houses Prefects or lastly by the Headmaster. Please try the frist two before trying the last.
You cannot and should not try to get into another Houses Common Room as this is against the Rules and you can end up in Detention in the Dark Forest. No breaking of the Rules is tolerated! So please make sure that you have read all of the rules on the Rule Page which can be found in the Castle.