When I attended C2C: Country to Country, I photographed some parts of The O2's interior:
As can be seen here, the building is effectively a giant tent. This is one of the twelve towers that support the dome.
This is of an unused area of The O2. It might be used during other events, but as of this picture, it was empty; the openness of this section made it extremely cold and windy. The tent-like quality of The O2 is more present here.