I scoured the internet to buy skip-the-line tickets to Schloss Charlottenburg, which I'm told are 12 euros apiece, without any success! The spsg.de website is trying to sell the premium day ticket worth 19 euros covering the above site as well as a few other palaces, but since I'm not going to be for too long in Berlin, I will limit myself to Charlottenburg. Could anyone please direct me to the website, if there is any such, from where I can purchase these advance tickets? I just don't want to take a chance by leaving it till the day of visit.
Many thanks in advance.