Let $U \subset \mathbb{R}^n$ be an open and connected set. We assume there is a vector field $F \in \mathcal{C}^1(\overline{U})$ giving rise to a DS ($\overline{U}$ denotes the closure) $$\dot{\mathbf{x}}=F(\mathbf{x})$$ We set $\Gamma_{\mathbf{x}_0}=\{\mathbf{x}(t)|t \in I_{max}\}$ where $I_{max}$ is the maximal interval of existence.
My question is the following: Is there a DS/ can somebody give an example of a DS which has a dense trajectory in $\overline{U}$, i.e. $\overline{\Gamma_{x_0}}=\overline{U}$?
I am unable to come up with an example and wonder if something like this actually exists.