1. Locate the Metro Station: In the main game of Fallout 3, travel to the northwest corner of the map and search for the "Bailey's Crossroads Metro Station."
2. Enter the Metro Station: Upon reaching the Bailey's Crossroads Metro Station, enter it.
3. Find the Ticket Machine: Inside the Metro Station, look for a ticket machine near the entrance.
4. Purchase a Ticket: Interact with the ticket machine and purchase a ticket to "The Pitt." You can find this ticket listed under the destination for the raider camps.
5. Take the Subway Train: With the purchased ticket, use it on the subway terminal next to the machine to enter the subway. This will trigger a cutscene, prompting the subway to take you to The Pitt.
6. Arrive in The Pitt: After the train journey, you will arrive at the outskirts of The Pitt. From there, you can start exploring and completing the quests associated with the DLC.
Remember, to play The Pitt DLC, you must have the Fallout 3 game and the DLC installed on your gaming device.