Lots to do in San Antonio. My mom lives there, so we've visited many times over the years.
I'm assuming you will do some homework (I generally use TripAdvisor) to find the popular attractions in San Antonio. Here are some additional ideas that you might not come across and some day trips. These will require a car.
In no particular order:
1. Schedule a factory tour of the Toyota truck plant - all Toyota trucks are manufactured at the San Antonio plant. We lucked out when we visited. No one else was there, so we had a private tour.
http://www.toyotatexas.com/index.php?option=com_content&view=article&id=7&Itemid=2
2. Most people know about the Alamo. But there are 4 other missions south of the Alamo that form San Antonio Missions National Historic Park. As I recall, we started at the visitor center at mission #2 (Mission San Jose). It was then a short drive back to mission #1, and then we went south to missions #3 and #4.
https://www.tripadvisor.com/Attract...tional_Historical_Park-San_Antonio_Texas.html
3. Do some searching on the painted churches of Texas. German and Czech immigrants came to Texas in the mid 1800s in search of cheap land and, missing their homeland, built small European style churches. There are four churches clustered close together around Schulenberg. Here's a link:
http://www.texasescapes.com/CentralTexasTownsSouth/PaintedChurchesTour.htm
It will be about 1 1/2 or so hours driving time from San Antonio to the Schulenberg area. We started at Saint Mary’s Church of the Assumption in Flatonia and visited the 3 others in the nearby area. Then we looped back (a little bit out of the way) through Shiner to visit a 5th church in Shiner (Saints Cyril and Methodius Church). Also in Shiner is the beer factory. The European immigrants missed their home beer, so a brewery was started to brew European style beer. You can tour the beer factory (I'll admit that I've been on better brewery tours) and then sample a bunch of their beers. We like darker beers, and they do brew pretty good beer. I'll warn you that the serving sizes are generous. We drank half our beer samples before the tour and the other half after the tour. I'm glad we did. Had we drank all of the samples after the tour, we would have been too loaded to drive safely back to San Antonio. If I remember, the beer factory tour cost something like $5 per person. We visited these churches + the beer factory on our last trip to San Antonio - it was a very full day. These are active churches, so don't plan this for a Sunday.
One warning: once you get off the I-10, you are in rural Texas. My cell phone signal (Verizon) faded quickly and I lost Google maps. Fortunately, our rental car had a GPS that helped us get around. So if you want to plan a tour of the churches, make sure you have a GPS that will work or bring along maps to help guide you.
4. Day trip to Fredricksburg - Spring should be a nice time of year for this. To get you started:
https://traveladdicts.net/things-to-do-in-fredericksburg-texas/
https://www.fredericksburgtexas-online.com/plan-your-trip/willow-city-loop/
If you're a hiker, I've read that Enchanted Rock is a nice place for hiking, but I've never been. Also, if you are into wineries, there are a number of wineries in the area, but I've never visited. And there's another painted church in Fredricksburg. Look up how long the drive will be to Fredricksburg.
5. Spring should be a nice time of year to consider any of the following: San Antonio Zoo, Japanese Tea Gardens, San Antonio Botanic Garden. I'm pretty sure you'll come across info on these as you search San Antonio attractions.
6. You can check if a visit to Austin would interest you.
Have fun planning your trip. For me, planning is part of the fun.