Although it has seen significant changes and gentrification in recent years, the Montrose neighborhood of Houston is still regarded as the LGBT center of the city. It is home to the largest concentration of LGBT bars in Houston.
Mary's is perhaps Houston's best known gay bar. It operated in the heart of Montrose from 1970 until 2009 and featured a beloved mural by Scott Stoveland depicting long-time bar patrons. The mural was restored and then painted over in 2011 as the building was remodeled to become a coffee shop.
Inside/Outside was a piano bar that opened in 1974. It is notable for being the first location of Town Meeting 1, a forum to discuss LGBT issues in Houston and begin organizing services for the community. The meeting was moved to the Astro Arena and took place on June 25, 1978. Inside/Outside later became EJ's and was open until 2014.
The Montrose Mining Company opened in 1978. It is still in operation today and is now Houston's oldest gay bar. Three other bars (The Tattooed Lady, Pacific Street Station, and Uncle Charlie's) operated at the same address prior to the Montrose Mining Company.
Sources: Houston LGBT History: http://www.houstonlgbthistory.org/houston-marys-outsmart.html, http://www.houstonlgbthistory.org/misc-mining.html