  We propose helical trilayer graphene (HTG), a helical structure featuring
identical rotation angles $\theta\approx 1.5^\circ$ between three consecutive
layers of graphene, as a unique and experimentally accessible platform for
realizing exotic correlated topological states of matter. While nominally
forming a supermoir\'e (or moir\'e-of-moir\'e) structure, we show that HTG
locally relaxes into large regions of a periodic single-moir\'e structure in
which $C_{2z}$ is broken, giving rise to flat topological bands carrying
valley-Chern numbers $C=\pm(1,-2)$. These bands feature near-ideal quantum
geometry and are isolated from remote bands by a large gap
$E_{\mathrm{gap}}\sim 100$ meV, making HTG a promising platform for
experimental realization of correlated topological states such as integer and
fractional quantum anomalous Hall states in $C=1$ and $2$ bands.
