The dungeon is shows under constructions forever. I am currently level 22 and the dungeon has still been under construction I do not know how to unlock it.
Topic on Guide:Wiki Support< Guide:Wiki Support
Clock Work dungeon showing under construction
For game related issues you'll have to contact customer support. And it's called Bottomless Dungeon now, this replaced the Clockwork one.
For gameplay issues please contact Gameloft Customer Care, for complaints and suggestions please post in the official forum of the Game owner (Gameloft).
This is the Wiki - created and maintained by the user fanbase (you, me, all players who like the game) - and it is not officially linked to Gameloft.
In the GameLoft Forum, Community Managers (like Adam e.g.) might provide some feedback on this issue, here it will stay unheard by those who could change the game.