You are the dark knight, the shadow, the vengeance, you are Murk Man! Now the only thing you are missing in your heroic crusade against the criminals of Night City is the Murk mobile. Corny intro aside, this is a batman reference in the game, which also gives you a very fast car and a legendary clothing item for free.
Finding the Murk Mobile
Get to the marker on the map and go through the cave until you find a container with a light next to it, you can find the car and the message left by Murk man. The car is saved in V’s “call a vehicle” menu as Caliburn.