Paseo del Rio (river walk) in San Antonio.
This town has a real treasure, which is probably the envy of most other places in Texas. The San Antonio River runs in a close loop below street level, and there are walkways next to it almost all the way round. Take a few steps down, and you're in a completely different world. It's a cool and relatively quiet place, where the water and trees provide the feeling of an oase shutting out most of the traffic noise from above.
Many restaurants have established terrasses down here, so you can still enjoy the benefits of civilisation... At night, many of the buildings and trees are illuminated, making it even more romantic. The only nuisance are the narrated boat tours, which create unnecessary noise for those not riding with them.