Definition of grottos:
(n) :
A small cave.
(n) :
An artificial cavern-like retreat.
(n) :
A Marian shrine, usually built in a cavern-like structure.
(n) :
(Philippines) A garden or roadside shrine with a small cave containing a statue of the Blessed Virgin Mary (usually Our Lady of Lourdes and sometimes paired with a water feature)
(n) :
A local organization of cavers that typically organizes trips to caves and provides information and training for caving; a caving club.
(n) :
(Satanism) A secretive name for a local group of underground Satanists.