To Tantalia

Test Chamber 13: Place portals as shown to redirect the laser. Use a time portal to move the laser into the future. Travel through the time portal (taking damage is acceptable) to reach the future. Rearrange portals in the future to direct the laser into the target, then exit through the door.

Test Chamber 14: Travel to the present via a time portal. Summon a reflector cube and position it in the present as indicated. Use a portal to direct a laser through the first node, then use this to reflect the laser into the next two nodes. Travel to the future. Use portals to bring a laser into the present through the time portal, ensuring it passes through the current node. Retrieve the reflector cube from the future and bring it to the present. Ensure the present reflector cube hits all three nodes; adjust as necessary. If the future reflector cube was moved, return to the future to retrieve it. Position the future reflector cube to reflect the laser into the receiver, completing the chamber.

Test Chamber 15: Start by going through the particle field to the left. Place a portal where the laser hits the wall and a time portal on the opposite wall. Travel through the time portal to the future to bypass the particle field. Head to the other side of the room and use another time portal to return to the present, now on the other side of the field. Place a new portal on the upper wall so the laser hits the first receiver. Return to the future and place a portal on the small wall in the laser room to shoot the receiver. Return to the present; the laser should still hit the upper receiver, powering an elevating platform. Stand on the platform and shoot a time portal behind the node. This raises the platform, allowing you to summon a reflector cube. Place this cube on the lip above the second receiver. Travel to the future. Retrieve the future reflector cube and enter the laser room. Place another time portal to bring the future reflector cube into the present laser room, positioning it to reflect the laser to the second receiver through the node. To bypass the particle field, use an existing portal or a time portal. You need to be in the present on the other side of the particle field. Climb the stairs and use a portal on the upper wall to hit the third receiver. Finally, move the reflector cube onto the switch to complete the chamber.