watchtower (n.)

• beacon
• belvedere
• bleachers
• bookmark
• bridge
• cairn
• gallery
• gazebo
• grandstand
• landmark
• lighthouse
• lightship
• lookout
• loophole
• mark
• marker
• menhir
• milepost
• milestone
• monument
• observatory
• outlook
• overlook
• peephole
• pharos
• platform
• ringside
• tower