In the museum, while chasing the Chairman with Alyssa, you will enter an exhibit that shows the burial customs of the Gozerian Cult. Once you enter this room, quickly turn to the right and you will see three portraits in the dark. Use the Stasis Stream to illuminate the painting. You will see a skeleton creature kissing a woman, but he has pulled up her dress and appears to be touching her.
While in the hotel ballroom with Slimer, press by the piano to occasionally hear the same notes that Peter played in Dana's apartment in the first movie.
In the Sedgewick Hotel level, you will pass room 1204 while hunting for Slimer. Inside can be heard the original Ghostbusters commercial from the movie. This is also a reference to Dana Barrett, who had a habit of leaving her television turned on too loud.
The portrait of Ivo Shandor's mother we see on Shandor Island is in fact modeled after Francois Boucher's 1750s portrait of Madame de Pompadour, courtesan to Louis the XV of France. Though a political and historically significant figure, she was pretty much a prostitute.
Check your messages when you get back from the Stay Puft Marshmallow level. The new person's father or friend says "You're doing adequate work out there Luke, keep it up!", revealing his name to be Luke Hoss.
Go upstairs at Ghostbusters headquarters to find a drawing by a child on pink paper hanging near some electrical equipment. The text "To Uncle Egon, from Ed." Appears on it. This is a reference to the fan fiction Ghostbusters videos "Freddy vs. Ghostbusters" and "The Return Of The Ghostbusters" which features Egon's nephew Ed Spengler.
To unlock this achievement without having going through Story mode a second time, acquire amemory card and a hard drive. With a completed saved game file on your hard drive, start a new game on your memory card. Play past the training mission and save the game as soon as you get into the hotel mission. Then, quit the game. Load the saved game file from the hard drive and go to the final Boss. Go into the "Options" menu, then to the "Game Play" setting and change the "Memory" setting to the memory card. Defeat the Boss and the achievement will be unlocked.
In Ghostbusters HQ, there's a table upstairs with a phone. Interact with the message machine to the left of it to listen to a variety of voicemail. There is new voicemail each time you go to Ghostbusters HQ.
The fountains can be found in the following locations:
At the firehouse.
After you enter the Sedgewick Hotel, the soda machine room on your right.
After the water drains from the hallway but before you reach the Sargassi Lounge, the corner of the elevator lobby.
In the laundromat Zeddemore breaks into at Times Square. By the cursed artifact, pushing bone, in the back room.
After the cut-scene of Hoss and Stanz and the two office workers in the elevator at Times Square, you will be at the architectural office. The fountain is at the corner of the hall.
In the Public Library hallway leading to the juvenile reading room.
After the Egyptian and Mummification exhibits at the Museum, Venkman will spring out to surprise Hoss and Zeddemore in a maintenance hallway. The fountain is there, right next to the Azatoth Head artifact.
When revisiting the Sedgewick, you need to turn the power back on at the generator room. The fountain is in the generator room.