Alhambra

The Nasrid palace is laid out so that you go tend to go through one way but you can go back into prior rooms. Once you exit this palace you are done - you can't go back in it but while inside you can double back to different rooms.

Note that the Nasrid is timed - you have to enter at your timeslot or you can't go in. They are strict on this.

The rest of the complex;

What the Alhambra is is a large complex with multiple sights. You buy one ticket that gets you in to all these sights called The Alhambra.

You can enter the grounds, the parador, and some sights like Charles V Palace without tickets anytime the complex is open. Other parts like the Alcazaba fort and Generalife Gardens require a ticket (all on the same ticket). You can see them in any order at any time while your ticket is valid.

The only thing I'm not sure about is if you can re-enter the Generalife or Alcazaba once you exit. You get your ticket scanned, go in, and can go to different sections at will. But once you leave the zone I don't know if you will be allowed back through the ticket check.

No you can't re enter Generalife and Acazaba.

There are several ticketed place in the Generalife and you can only enter each once and once you have made the circuit you cannot re-enter. some of the most beautiful parts of the Alhambra are there.

When I was there in 2006, once you had entered the Nasrid Palace, you could stay as long as you liked, and you could backtrack to revisit sections. However, you are "swimming upstream" against the other visitors when you backtrack, so I simply went all the way back to the beginning and saw the whole thing again. The Palace is indeed set up as a one way visit. Once you've exited, you definitely can't reenter.

This is the only part of the complex where things are in a linear order. For the other sections, including the Alcazaba and the Generalife Gardens, I don't recall any issues with wandering and seeing the parts that interested me as much as I wanted, or skipping sections that were of lesser interest.