We went to Schlitterbahn 2 summers ago for 10 days - had the most amazing time.
We stayed in one of the Schlitterbahn apts on the river - loved loved loved the water park.
Here are a few things we did:
Natural Bridges Caverns - amazing, we did the general cave tour and the flashlight tour. Then we went thru the drive thru safari where we had an encounter with an ostrich that to this day has us all rolling on the floor laughing.
We tubed the Comal with Rockin R tubes (we were their first ever NV guests that they could remember) the Guadalupe was running too high that summer and there was no tubing plus DD was only 8 and it scared us a bit.
Visited the Snake Farm (featured on Dirtiest Jobs)
The Alamo was worth dealing with the heat as was a visit to St. Francis Cathedral where the remains are entombed.
We took the boat tour of the Riverwalk and enjoyed the boat but didn't enjoy the commercialism of the Riverwalk, we did enjoy the outdoor market that is a few blocks away much more.
SeaWorld SA was fun
We took a sunset Bat Cruise up in Austin on Lady Bird Lake
Enjoyed dinner in Gruene at the Gristmill, and in Driftwood at the SaltLick.
Wandered to LockHart one day for Blacks BBQ
We had dinner at the "famous" Oma House and while dessert was fabulous, dinner left us hungry. We were surprised at the cost (spendy) vs. the portions and literally left hungry.
We loved our TX vacation, have fun!