How do I unlock the pier in CityVille?

This page has a list of all the quests and what you need to do to complete them. The Pier is near the middle of the "tree", right after build a school. It requires you to have 3 expansions and lay 3 roads.

The Zynga forums have a huge thread about this particular quest not unlocking for people. The solution that is offered again and again is to clear up other quests that you have been assigned. Apparently there is a limit to the number of quests you can be assigned at one time, which means the Pier quest (or one of the ones leading up to it) might be blocked. So if you haven't seen the quest yet, just keep working on other ones you have and it should eventually show up.