I haven't been to the Hoover Dam since I was a kid. On our way from Vegas to Grand Canyon we decided to do a short pit stop to view the Hoover Dam.
Parking in the structure will cost you $7. You really have no other choice but to pay. At first we went to the visitors center...you have to go through security and a metal detector and get all your belongings scanned, then it will cost you to get into the visitor's center. I thought it would be free. So we ended up skipping tours and visitor center, because I feel you can just read about it and walk on your own, which is exactly what we did.
We walked around the dam and enjoyed the views of lake mead and the energy plant. The fun part is standing on the border of Arizona and Nevada!