"G. gigantea" is, as its name suggests, a huge antpitta. Length ranges from and weight is up to , which makes it easily the heaviest of all tracheophone suboscine birds – its nearest rival, the chestnut-throated huet-huet, is not known to exceed . Its back, wings, and the stubby tail are dusky olive-brown. The top of the head is pale to medium grey, running down to the neck. The remaining plumage is deep rufous-brown. The throat and breast feathers are black-edged, resulting in a dark barring in these regions. The bill is dark, strong and heavy; the eyes are likewise dark, while the legs and feet are grey.