<image> As shown in the figure, point 0 is the gate of a park. Inside the park, there are 9 attractions A_{1}, A_{2}, ..., A_{9}, and the roads between the attractions are as shown in the figure. Tourists can only travel from one attraction to another in the direction indicated by the arrows in the figure. After entering the park gate, tourists can visit some or all of the attractions according to the above travel requirements. Once they return to gate 0, the visit is over (each attraction can only be visited once). How many different routes can tourists choose for their visit? ____ routes.