I have to say that this took me a bit to find and I actually had to backtrack to find this museum. It would seem obvious about the aquaduct being hard to miss but with Lisbon's hills and multiple story buildings, I did not see the aquaduct from the street I was on. I seemed to have it in my mind that you could walk along the aquaduct but when I found the entrance to the "museum" this was not the case. I put museum in brackets as I did not find very much information in the building. Paying €5.00 to enter, I wandered slowly around the giant pool of water, glancing at the photos on the wall. They had no information or description so I was not sure what I was looking at. The large room was pretty cool with the water reflecting the vaulted ceiling. It took about ten minutes or so to walk to the other side where there was a staircase leading upwards.
Climbing upwards, I was thinking this would lead me to the aquaduct and I would get to walk along it. Nope. It just lead to the roof of the building. It did give a nice view over the fountain and the large pool of water though from the stairs.
The photo below is inside the aquaduct. No water! Guess Lisbon has updated it's plumbing system.
Up the stairs to the roof, I admired the view and wished for the sun to come back. I have mixed feelings on this museum. I liked the building, I liked the water but I didn't like paying €5.00 for something I didn't understand and only took in for less than half an hour. Reading the tripadvisor reviews for the place leaves me with even more mixed feelings with people praising the place. Googling now I think I got the Water Museum and Aqueduto das Águas Livres confused. I had marked the water museum on my map app and thought that would be it and walking there realised it was not.
I still have a few more days in Lisbon so who knows, I might end up at the Aqueduto das Águas Livres.