While spreading the word of Pan's death and trying to recruit nature spirits for the impending war, Grover is knocked unconscious by Morpheus. He is asleep for several months and is awoken with his empathy link when Percy Jackson and Nico di Angelo search for the second entrance to the Underworld. Once he is awake he explains why he was in Central Park to begin with and then opens the entrance to the Underworld with his reed pipes.
|Magical Locations:||Aeolia | Camp Half-Blood | Camp Jupiter | Cave of Trophonius | C.C.'s Spa and Resort | Daedalus' Workshop | Lotus Hotel and Casino | Mount Othrys | Ogygia | Olympus | Pan's Cave | Sea of Monsters | The Labyrinth | Tartarus | Underworld | Waystation|
|Cities, States, and Towns:||Alaska | Bar Harbor | Bologna | Chicago | Detroit | Gila Claw | Indianapolis | Jamestown | Montauk | New Mexico | New York City | Palm Springs | Quebec | San Francisco | Dalmatia | Vancouver | Venice | Westport|
|Other Locations:||Apennine Mountains | Aunty Em's Gnome Emporium | Carlsbad Caverns | Crusty's Water Bed Palace | Empire State Building | Gateway Arch | Grand Canyon | Greece | Hoover Dam | Italy | Junkyard of the Gods | Mount Diablo | Mount Etna | Mount Saint Helens | Mount Tamalpais | Pikes Peak | Polyphemus' Island | ROFL | Rome | Triple G Ranch | U.S.A. | Waterland|