The Reunion

The Reunion is a main quest in the Fallout: New Vegas add-on Lonesome Road.

Quick walkthrough
Travel to the Canyon wreckage near Primm and enter the Divide.

Detailed walkthrough
You will get a radio signal from Ulysses telling you that he wants an ending to things. Go to the Canyon Wreckage and enter the Divide.

The Divide can be reached by traveling a north by northwest path from the California Sunset Drive-in.