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 guest house itself is right outside the green zone.
If you want to buy an environmental badge use this link: Buy Environmental Badge. The online order costs 9,90 Euro.