Artyom must reach the lighthouse. Read this chapter to know the way.
Enter the car and drive to the lighthouse. After reaching it, enter the nearby cave. Inside, use the rope to reach the opposite side. Keep crossing the bridges. Eliminate/stun enemies. Later, you will come across a small group of enemies - they shouldn't be a challenge for you.
You finally reach the surface. Keep moving up, towards the gunshots. You encounter a group of bandits attacking the lighthouse. Kill them and then wait for Giul to lower the boat (serves as a lift). Reach the top and listen to the woman.
Use the nearby workbench. Refill ammo and medkits. Follow Giul - the woman will lead you to an old bunker. The woman asks you to restore the power. The switch is in the next room. Giul will now send you to the undergrounds to retrieve satellite maps.