Are the on ground tours good? The Steve's book indicates that they are "uneven". Also, is the aqueduct claustrophobic? I can't tell by pictures. I'd like to hear from someone who has done this site!
Nothing claustrophobic about the aqueduct. I didn't do a tour but found it easy to explore the entire site on my own.
No guide needed and no claustrophobia at all.
Climbing up the stairs to the aqueduct can be a bit weird for people with claustrophobia. It's dark and tight but you're not in that part for very long so you should be good. If memory serves, there are parts along the walk across it that are dark and tight but again, very short period of time. Turn on your mobile phone flashlight if it makes you uneasy, that's what some of us did.
I did the guided tour earlier this month, it's the only way to cross inside the aquaduct. No problems with it, but then I'm not claustrophobic. I AM 6'4 tall, so I did notice the lack of headroom somewhat, but it was ok. 4 or 5 of the covering stones have been removed to give occasional relief.
Understandably, the stone underfoot inside the aqueduct isn't totally even - you wouldn't expect that after 2000 years - but it presented no issues.