Castlevania: Legacy of Darkness is a 1999 action-adventure game developed and published by Konami for the Nintendo 64. A prequel and expanded version of Castlevania, also released on the Nintendo 64 earlier the same year, it contains a revision of the original game with improved graphics, added villains, and alternate versions of some levels.

A large part of the game's challenge is based on jumping from platform to platform while avoiding environmental hazards, such as enemies and traps. Platforms are usually stationary, but some may rotate out from under the player, move through the environment like a rail shooter, and crumble or fall away underfoot. There are some invisible platforms that either afford players a strategic advantage or lead to hidden items.

Castlevania includes elements from the survival horror game genre. In addition to the trappings and narrative devices of Gothic horror, players are often placed in situations that evoke feelings of stress, anxiety, and vulnerability. Players may be trapped in caged fights with monsters, such as the battle with the Cerberus hounds in the Villa when the screen darkens to near-black. Some caged battles are timed, such as the boss battles in the Duel Tower level, where the player will be crushed by a falling ceiling should they not best their enemy in time. Vampires are often fought in caged environments, with the added complication that they can latch onto Carrie, Cornell, Henry and Reinhardt to suck their blood. If the player does not break free by rapidly rotating the control stick, the character's status changes to "vamp" and they will not be able to use their primary weapon or healing items. Unless a specific item is used to recover, the game becomes exponentially more challenging. Legacy of Darkness features two high-stakes survival horror sequences: In the Villa's maze garden, players must help Henry through the labyrinthine hedges while strong, unbeatable enemies give chase. In the Castle Center, players must carefully carry the "magic nitro" item through a nerve-wracking obstacle course to its destination. One fall or hit can cause the volatile chemical to explode, resulting in immediate death.

Set in the year 1844, the game stars the man-beast Cornell in his quest to prevent his adoptive sister, Ada, from being used as a sacrifice to resurrect Dracula. The game opens as Cornell arrives at his village, which has been burned to the ground by Dracula's minions. He finds Ada's pendant in a doorway and follows her scent to Dracula's castle.

During the course of the game, Cornell comes upon a grand estate owned by the Oldrey family: J.A. Oldrey, the master of the Villa, Mary, his wife, and Henry, their son. Gilles de Rais and Actrise have turned Oldrey Senior into a vampire. At Mary's request, Cornell guides Henry to safety. Later in life, Henry returns to Castlevania to save kidnapped children.

Throughout the game, Cornell encounters his rival and fellow man-beast, Ortega. Ortega has allied himself with Dracula to finally beat Cornell in combat, turning into a chimera like creature. They eventually battle near the end of the game, just before Cornell defeats Dracula and saves his sister. He only accomplishes the latter by sacrificing his man-wolf powers. Unbeknownst to the hero, acquiring this power was the true aim of the dark forces, as it was the perfect sacrifice (not Ada, as Cornell had assumed) to resurrect Dracula at his full power.

Legacy of Darkness is a continuation of Konami's first attempt of Castlevania, also published in 1999 to create a 3D Castlevania. For example, Cornell was present in early development media and press information for Castlevania, but was ultimately removed before the game's release.

Legacy of Darkness's primary focus is on a new story (a prequel to Carrie and Reinhardt's adventures) in which Cornell explores new levels, as well as redesigned levels from Castlevania. Levels from Castlevania that have not been drastically changed (such as the Villa) are often navigated in a new or novel manner and feature different puzzles. Completing the game once unlocks Henry's quest, and he explores his own set of levels and new bosses. Many are redesigned levels from Castlevania.