The architect achievement is obtained by receiving 100 upvotes on landmark plaques that you place on structures you create. Upon completion, a player will be 20% of the way to the master architect achievment.
Master Architect Achievement
Get 500 votes.
Receiving votes on landmarks is directly related to the amount of traffic near your landmarks. Landmarks in isolated locations will generally get fewer votes than those in populated areas. Placing a teleporter by your landmark is also advisable, as this will let people visit more quickly.