To solve this problem, we must visualize the park in our mind. It is a large rectangle. The rectangle can be divided into two right triangles if it is split from corner to corner, each with a 20 km side and a 5km side. The length of the pedestrian route is the third side of the triangle. We can use the Pythagorean Theorem (a squared + b squared = c squared) to discover the length of the third side. Thus 20*20 + 5*5 = 425. The square root of 425 is 20.62 km. The pedestrian route is 20.62 km.