The ANNIE detector sits in an underground hall at Fermilab. The neutrino beam impinges from the left. The detector consists of three main elements: (1) a front veto to reject charged particles from neutrino events occurring upstream of the hall in the dirt, (2) an instrumented tank containing 25 tons of gadolinium loaded water to serve as both the neutrino target and neutron tagger, and (3) an iron and scintillator sandwich muon range detector to track and range out muons from the neutrino interactions in the target. Image: ANNIE collaboration