When I was a kid I had easy access to Disneyland, Knott's Berry Farm, the Hollywood Wax Museum, Magic Mountain and the beach. Still one of my favorite places was Carlsbad Caverns.

Carlsbad Caverns National Park via Facebook

Carlsbad Caverns National Park is having "Free Free Days".  You've missed the MLK opening, but there are three more days to take advantage of. It's free to visit 4/21 for the first day of National Parks Week, 9/22 for National Public Lands Day and on 11/11 for Veterans Day.

The usual admission is $12 a piece for adults and free for kids 15 and under, so it's still kind of a steal for a whole days adventure. They actually have an event invite if you'd like to find out more. You can also visit their website here. Carlsbad is just a hair under a three-hour trip from Lubbock, so it's extremely doable as a day trip.