If you climb the ruins, be aware that the descent can be visually disorienting. Do not climb the Acropolis if you are subject to vertigo.
The area around the site seems quite safe.
Vendors near the site may direct you to park next to their shop and may pressure you to pay them to watch your car. If you do not desire their services, you may safely turn them down.
fees/permits
Admission fee is 58 pesos October 2010