Willow, you can't open that door yet.
Cerio told you to start your investigation in the Grotto delle Felci. In this game, it's always best to do as people tell you.
You can find the grotto on the map. You can only get there by bus. So you need a bus ticket, and money to buy it, and a code to use your creditcard. You can find the code in the real world.
Spoiler:there's a piggy bank next to the computer
