Not wanting to draw TOO much attention to the fact that the Prince was out and about with Riku, or really draw attention to Riku, only Frank followed after the two. He could be written off as guarding the Prince in these dangerous times, not as making sure the Prince and his Beloved did not do anything inappropriate.
"As you wish," Riku said pleasantly, refreshed from lunch and the private time with the Prince. "Its this way." He started down a hallway that led towards the outter wall, and then up a winding staircase. "Our guide said that this is one of the watch towers. There are four... one in each direction. But we only saw this one. It looks back towards Hollow Bastion."