N.B. Foxington only becomes available after beating Jinx and completing the story. Once the Credits have been watched you will be taken there.
To the north-west of the map you will find the 3 levels you need to beat.
The Fluffle Shuffle
Gotta Get Back In Time
Two of the levels involve beating bosses from earlier in the game, with an increase in difficulty. The 3rd level Wrigglemania sees you compete through 4 waves of different enemy combinations.
Near the spawn point within Foxington, just to the right of Lyra (the other fox) you will find a map showing the location of all levels - these are the red dots.