The tallest mountain in Barcelona is Tibidabo, and it is about 500 meters high. Right at the top there is an amusement park that is also called Tibidabo, and is one of the oldest in Europe.
It is a good way to spend a whole day in family and children will love it. Being on the mountain has two advantages: it is much less hot than in the center of the city, and has spectacular views of all of Barcelona.
On their website you have information about the tickets, schedules and how to get there. The easiest way is to take the T2A bus in Plaça Catalunya (look for a Desigual store), which in half an hour will leave you at the entrance of the amusement park.
First you will find a couple of free attractions: some cool slides …
…and some water games.
Then there’s the so called “panoramic area” where you’ll find some rides for young children (from about 2 to 5 years). You are free to walk on this area, and only have to pay to use the rides (individually for each ride, or unlimited access for the panoramic area).
And then there are more levels with more than 30 rides for all ages. Kids from 5 years old onwards will have a great time there. You’ll need to pay the “general admission” fee to go there.
There’s a classic ride called “Embruixabruixes”, don’t miss it! Especially magic at night.