Red Redemption

How do you unlock Red Redemption?

In The Binding of Isaac, Red Redemption is unlocked by unlocking Tainted Jacob.

The starting room spawns with no rooms connected to it. Rooms spawn in clusters around the map and must be found via the Red Key. While the Red Key can be used an infinite number of times, it has 20 uses before Dark Esau spawns. Each subsequent 5 uses will spawn another Dark Esau if Tainted Jacob has yet to turn into his lost form. The Red Key cannot be used to open doors to I AM ERROR rooms. Each floor generates as a labyrinth floor, with one shop, and two item and boss rooms, except the fourth floor, which has only one boss room. All rooms may be from any floor of the current chapter.