What is a must see along the way from Maryland to Austin Texas

Multiple routes to go; depends how far south you want to go first. You can go through Atlanta - see their phenomenal Georgia Aquarium; you can take another route thru Tennessee - see Chattanooga - add Nashville as side trip - take you near Dallas for some great sites there; you could go way south and divert little ways to New Orleans (also do Destin) . While in Austin, head to San Antonio for The San Antonio River Walk, stop in New Braunfels  or Fredericksburg (Texas) for ethnic German food and architecture, and the Schlitterbahn Waterpark!