It‘s the dirtiest city in Europe.
It‘s the most popular holiday destination in the world.
Use the + superlative adjective to say which is the biggest, etc. in a group. After superlatives we use in + names of places or singular words for groups of people, e.g.
It‘s the noisiest city in the world.
It‘s the most beautiful city I’ve ever been to.
It‘s the best fiIm I’ve seen this year.
We often use the + superlative adjective with the present perfect + ever.
|beautiful||more beautiful||the most beautiful|