The most natural way of saying it would be:

… quand j’aurai vu tout ce qu’il y a à voir…

With:

• voir over regarder
• tout ce qu’il y a à + verb

This is another very natural way to say that, despite it being more informal :

Je serai de retour quand j’en aurai fait le tour

I guess a more idiomatic way to say it would be :

... quand j'aurai tout vu de cette ville.

Without the repetition, you imply that you mean “everything possible” within this context (i.e. everything you would be able to see).

I join @AlexisLeGal on his answer. The expression “faire le tour de” is often used in various context and means that you have (or need to) covert the subject.

Il est nécessaire de faire le tour de la question.

Could be translated by

It is necessary to deal with every possibility.

But it’s a very “context-wise” expression.