Before visiting the ruins please jot these four things down.
1) Wear sneakers not flats.
2) Bring bug spray and a hat.
3) Bring cash.
The park only accepts cash. You will also like to have some cash handy for snacks and to rent a bike, be chauffeured on a bike cab or buy snacks.
Trust me, you will 9/10 want to be chauffeured because it is a long walk to the ruins once you are inside the park and it is extremely hot.
4) Arrive early to beat the crowd. The ruins close at 5.