If you have an iPhone, open the camera as if you wanted to take a picture, point it on the QR code and wait a couple of seconds. At the top of the page you will see a link for your visit on the interactive guide.
If you have an Android phone open the Google Play Store app on your smartphone and install any app capable of reading QR codes. 
We can recommend Barcode Scanner, which is free and without advertising. If you decide to use Barcode Scanner, please note that the identification of the QR Code works with the phone turned horizontally.