Interesting to see this old tunnel/aqueduct, and thinking how much work it must have been to dig this tunnel without machines. The "tour" is basically walking the first 400m of the tunnel until the midpoint where the two tunneling teams met; and going back. It is still fascinating to see, especially sections where you can see the lower part of the tunnel some metres below through metal grating. You get to wear a hardhat which is a good idea because you are going to bump your head on the ceiling, no matter how much care you take.

Before doing this tour, be aware:

• especially the beginning is very tight and narrow.
• there are longer stretches where walking upright is impossible for most people
• the floor is uneven and slippery, plus there are darker sections.
• half the floor in many places is metal grating with a sharp drop beneath

So if you are scared of any of these things better stay out of the tunnel, you wouldn't have much fun.

Unfortunately, the guide was not really in a mood to say anything about the tunnel besides warning of slippery sections and telling people not to use flash when taking pictures. Some facts or at least a greeting at the start would have been nice. There are also no other sources of info around, a missed opportunity to teach visitors some more about this early engineering achievement.