The Ancient Light (太古の光 Taikonohikari?) is a Level Up Item that can be obtained by Sonic in Sonic Adventure and Sonic Adventure DX: Director's Cut, and by both Sonic and Shadow in Sonic Adventure 2 and Sonic Adventure 2: Battle.
The Ancient Light is a hovering white orb of light that is absorbed into the body of those who touches it. Obtaining the Ancient Light allows the user to perform the Light Speed Attack, an attack that destroys multiple enemies at once.
In Sonic Adventure, the Ancient Light is located in Mystic Ruins when Sonic has to proceed to Red Mountain. To obtain it, one has to go into the cave that appears in front of the train station at Mystic Ruins and go through the tunnel until Sonic reaches the other side. With Angel Island to the left, the player must pass through the field until Sonic gets to the entrance to the bridge leading to Angel Island, and the Ancient Light will be located on a flat rock platform to the left of the bridge entrance. With it, Sonic is able to proceed onto Red Mountain, by destroying the Kiki guarding it.
Sonic Adventure 2
Sonic the Hedgehog
Sonic can find his Ancient Light in Green Forest, which serves as an optional Level Up Item. After the second time Sonic needs to swing on vines and after coming through the second loop (half loop), he has to hit the springs and land on the desired platform. Once on this platform, the player must go to the right and there will be a 10 rings Item Box. The player must go to the nearest edge and a Mono Beetle should appear. The player must then use a series of Homing Attacks on it and the Item Boxes that appear behind it to reach another platform, where the Ancient Light is located.
Shadow the Hedgehog
Shadow can find his Ancient Light in Sky Rail, which serves as an optional Level Up Item. Left from the first Chao Container, which is located on the platform to the left, before taking the first rocket up, is a line of Mono Beetles. One needs to use the Homing Attack on them until Shadow reaches the spring on the other side of the pillar, which leads up to the Ancient Light on top of it.
- In Sonic Adventure 2 the Light Speed Attack is an optional upgrade that simply makes large groups of enemies easier to fight. While it is impossible to proceed to Red Mountain without the Ancient Light in Sonic Adventure (unless the player uses glitches to pass through the wall), it is not required to complete any levels
- It is the only Level Up Item in either game not to appear visibly attached to Sonic and Shadow's bodies in any way.