Since 01.01.2008 Berlin has a so called “Umweltzone”, i.e. environmental or green zone. Since 01.01.2010 only cars with a green badge are allowed to drive in certain parts of the city. The zone can be found here: Green Zone
However you are allowed to drive to the guest house without a badge when you manage to avoid driving through the zone. The guesthouse itself is right outside the green zone. If you want to buy an environmental badge use this link: Buy Environmental Badge.