Do you know the tent map $T\colon[0,1]\to[0,1]$, look here? It's a piecewise linear map, with $T(0)=0=T(1)$ and $T(\frac{1}{2})=1$. It has this property, that if you iterate it, its graph will look like many peaks, and for any open subset $U\subset [0,1]$ there is $N\in\mathbb{N}$ such that for any $n>N$ we have $T^n(U)=[0,1]$. It's much stronger then topological mixing and if you take $\Pi^k T\colon [0,1]^k\to[0,1]^k$ it will also have this property, so you should be able to do the cube.