  We combine experiments and numerical simulations to investigate the low
energy states and the emergence of topological defects in an artificial
colloidal ice in the Cairo geometry. This type of geometry is characterized by
a mixed coordination ($z$), with coexistence of both $z=3$ and $z=4$ vertices.
We realize this particle ice by confining field tunable paramagnetic colloidal
particles within a lattice of topographic double wells at a one to one filling
using optical tweezers. By raising the interaction strength via an applied
magnetic field, we find that the ice rule breaks down, and positive monopoles
with charge $q=+2$ accumulate in the $z = 4$ vertices and are screened by
negative ones ($q=-1$) in the $z = 3$. The resulting, strongly coupled state
remains disordered. Further, via analysis of the mean chirality associated to
each pentagonal plaquette, we find that the disordered ensemble for this
geometry is massively degenerate and it corresponds to a frustrated
antiferrotoroid.
