Estrica Iina
Google
Was closed on May 1, so we returned the next morning.
It costs 4 EUR for adults to enter.
There is also a brief history near the entrance.
Unfortunately you can’t enter the tunnel itself, where water flew, but you can walk on top, with great view over the city.
Note, the wall is high enough, so not scary with little kids, however they either need to be taller to be able to see or need to be lifted.
Overall was a great experience.