Oasis Oasis is a settlement in the Capital Wasteland which is full of trees and green plants . It is located northwest of Clifftop shacks and north - northeast of Broadcast tower LP8 . Bird s can also be heard singing once inside the gate , suggesting that animal life has been flourishing here . It must be entered from the northwest . Background . Oasis was originally a mine , but after the Great War it became just another part of the wastes . That was until Harold and Bob , a uniquely mutated product of the Forced Evolutionary Virus ( or FEV ) , arrived . Harold hosted a tree growing from his head which he likes to call Bob and at times " Herbert " because , as he says , " Bob hates it . " The grafted human and tree eventually found themselves overwhelmed by Bob ' s plant needs and became rooted to the ground ending their travels through the Capital Wasteland region sometime after 2241 . Here , they were discovered by several people who began to worship Harold as a god , despite all his protests to the contrary . These few grew to be a small and sometimes exclusive cult known as the Treeminders . These dogmatic few began to form , in secrecy , a full religion . Bob began to blossom ( which Harold apparently finds embarrassing ) , and many plants grew in this area , which became green with life , a stark and dramatic contrast to the rest of the wasteland . When the player character arrives he or she is urged to talk to Harold . After a " cleansing ritual " held by the Treeminders , the player character meets with Harold . After learning his history , the player character is given the option of either killing him , increasing his fertility , or slowing it down . This is the main plot / quest element for Oasis , and each choice has its own repercussions with the Treeminders and can affect the player character ' s Karma . Layout . Oasis is situated almost at the top center of the map . It is surrounded by steep cliffs , and can be entered only through a small gorge by traveling west to east . The entrance is small and can be easily missed ; use the compass for assistance . The Grove . The Grove is a small part of Oasis that is surrounded on all sides by trees and cliffs . This area can only be accessed after the Lone Wanderer has taken part in the ritual . It is entered via a wooden gate that comes from the pavilion , after it has been unlocked . In the middle , the talking tree , uniting Harold and Herbert / Bob , can be found . To the south - east , a small radioactive pond can be found . If the Lone Wanderer dives in the pond , an Easy locked hidden underwater door can be seen , which leads to the damp cave . The Caves . The damp cave is a cave that connects the Grove with the sunken chambers . It is accessed via an easy - locked underwater door from a pond in the grove . Inside there is a small contaminated lake ( 5 RAD / sec ) with a few level dependent mirelurks . There are several junk items floating on the water of the small lake and on the bottom of the small lake . Several skeletons can be found under water . Notable loot . Sunken chambers . As one enters the sunken chambers , turning left and up in a small room one will find : Appearances . Oasis appears only in " Fallout 3 " . Bugs . It is possible that certain dialogue options will disappear after completing the main Oasis quest , making it impossible to obtain your reward . There is no known reason for this , but it may have something to do with certain dialogue choices made prior to completion of the quest .