This paper reports the existence of plasma caves, minima in the electron density located at 5–10° to the magnetic equator, in the bottomside ionosphere based on electron densities simulations from the International Reference Ionosphere (IRI‐2007) and clear evidences given by plasma density and drift measurements of the Dynamic Explorer 2 (DE 2) satellite during 1981–1983. The IRI simulations suggest plasma caves as daytime features (08:00–19:00 LT; length of 18,158 km in the longitudinal direction), that range from theE region up to about 300 km altitude with 10° (or 1100 km) width in the latitudinal direction. In situ measurements of the ion and electron densities probed by the DE 2 confirm the existence of the plasma caves at low altitudes of the EIA ionosphere. The unexpected downward and upward (or weakly and strongly upward) ion drifts at the magnetic equator and the two off equators seem to play an important role responsible for the plasma cave formation.