[Xemnas is not, precisely, exploring. Not in quite the same way at least. There is, no doubt, any of a number of things that could be worthy of exploration sooner or later, yes. But neither is there any immediate hurry; accordingly, what Xemnas is doing is less 'exploring' and more 'lurking atop buildings.'
Admittedly, he's not expecting to find one of the Keybearers engaging in physically-dubious parkour, but at the same time it's not entirely out of the ordinary, either.
That said, he makes no effort to approach either. Simply waits and watches - he's well aware that Riku will be aware of his presence, and he's willing enough to leave whether or not a confrontation ensues entirely in Riku's hands, for the time being.]
Wild Card
Admittedly, he's not expecting to find one of the Keybearers engaging in physically-dubious parkour, but at the same time it's not entirely out of the ordinary, either.
That said, he makes no effort to approach either. Simply waits and watches - he's well aware that Riku will be aware of his presence, and he's willing enough to leave whether or not a confrontation ensues entirely in Riku's hands, for the time being.]