Is Glenwood Cemetery Open to the Public? Can You Visit the Graves of Say Denton Cooley As Easy as 123?

As a fan of the Houston Texans, I will definitely visit Bob McNair's grave in Glenwood Cemetary. But I also learned a lot of famous celebrities such as Howard Hughes, Denton Cooley, Gene Tierney, and George Hermann are also buried in the same place.

How difficult would it to walkto the gravestones of Howard Hughes and other celebs? WOuld I have to do something like pass security guards or pay a fee to visit for example Gene Tierney's headstone?