In the city of Citate Di Ravello, you can find the logo of YouTube user NerdCubed graffitied on a wall.
At the Cima Leon: Centcom location, a rideable soapbox derby car can be found found near one of the exits of the base. The car is extremely fragile and will explode after taking enough damage, which is odd considering it is only made of wood and has no engine. At the coordinates 'N 40 48.040 E 5 42.045', Mario Frigo can be found sitting in one of these with an empty one next to him. Getting in it will allow you to race Mario down the hill.
While the game is installing it's still possible to play the game. The player will be transported to Boom Island, which is considered to be a kind of a testing ground for the game and is the furthest located island from the mainland in the game.
At the coordinates N 47.925; E 40.783 there are ruins with a set of statues circling a dead goat. If left unattended for a while, the statues seem to switch places. This is a clear reference to the Dr. Who villains, the Weeping Angels, which is a species of statue-like predatory creatures that only move when not seen.