"Keep yourself and and the Damsel alive for as long as possible!"
The Sun Room is one of the unlockable minigames accessible from the Scores Room.
To unlock this room, earn a Gold trophy score for Money earned in a single game.
Gold trophies require $200,000, Silver trophies require $100,000 and Bronze trophies require $50,000.
Note that the trophy is awarded for reaching the required threshold of money, even if you spent it before finishing the game.
The Sun Room is the most unabashedly hostile room in the entire game, throwing a series of increasingly dangerous obstacles at you including arrow, spear, and smash traps, bombs, vampires, and ultimately the Ghost. The objective is to keep yourself and the Damsel safe. Dying or allowing the Damsel to die will end the game.
Normally, vampires start spawning one at a time from the top of the room after around 50 seconds, and the ghost appears after about 90 seconds. However, it is possible to live indefinitely by forcing one of the two lower smash traps into the ceiling, and then standing under it while on top of the spear traps. This will prevent any bombs from dropping; neither the vampires nor the ghost will ever trigger. The arrow traps cannot hit you on top of the spear traps so long as the two upper smash traps remain in their original positions.
See: Unlockable rooms