The exit from the Ashton missile silo leads to the ground level of the Sunstone Tower. The interior has taken blast damage, with only two rooms narrowly avoiding destruction. Three levels must be ascended to access the Sunstone Tower roof. Pvt. Foster's personal journal part 1 of the Nostalgia challenge can be found in a duffle bag, south of the tower, surrounded by two mole rats.
A Chinese Army: Special Ops Training Manual - Inside the tower, on a bookshelf facing the wall (hidden from view) on the southeast landing up one flight of stairs from the ground floor interior entrance. It can be obtained by console commands, skillful application of explosives, or by going into third-person view, crouching in the right corner (near the edge of the bookshelf), looking at a forward/downward angle, and rotating slowly until it appears.
A RALPHIE poster for the Feel Like a Kid Again challenge can be found in the ruined room off the stairwell on the third floor inside the Sunstone tower. Another poster can be found outside the tower in the broken building across from the Third Street Municipal Building on the second floor, on a wall to the left of two file cabinets.
Ulysses can be seen watching the player character from a collapsed building on the cliff face to the south as they descend from the roof.