I would recommend sending the instructions in an Airbnb message or if that won't work for you, an email. We like to keep all communication on site so we use Airbnb messaging for everything. We have a generic check-in message that we send to every guest a few days before their arrival with instructions for check-in but we do not include specific directions to get to the building. I'd say 99% of people either look it up before hand or have gps/google maps on their phones. To prevent any confusion we let our guests know as soon as they book that they will be receiving the instructions a few days before their arrival.