It's not a wall, more like a moat with a drawbridge :)

The drawbridge is lowered every two weeks and that's when the team delivers and demonstrates the stuff they did during that time. This is also the time the stakeholders get to present the prioritised list of work that needs to be done during the next two weeks (Product backlog).

During the two week period if the stakeholders need to communicate to the Fort of Scrum, they can shout from the other side of the moat and the Scrum Master is the only one with access to the only tower in the castle where the shouting can be heard. The team has complete autonomy and peace to work for the two weeks.