Hat Yai or Haad Yai or Had Yai depending where you see it written is a very large city in the southern Thailand. It is a lovely city full of historical buildings as well as glistening metropolitan high-rises. Pedestrian paths that are level, not broken, not taken over by stalls, means that you can walk easily around the city.
There isn't a lot to do in Hat Yai, but if you are stopping off after the southern islands of Malaysia, consider going clothes shopping. The clothing stores in Hat Yai are fantastic, none of the normal touristy same same clothing you see everywhere but awesome vintage, funky, pretty, glitzy numbers that will not cost tourist prices.
We stayed one night in Hat Yai, we could have stayed more, but to be honest, the violence in southern Thailand in recent years, in particular, the bombings in Hat Yai city, made us a little uncomfortable when deciding to stop there. Now that we have been to Hat Yai, seen the place, felt the culture of the place, we would both go back there, and for longer too. It was a safe place, as safe a place in anywhere in the world.
We didn't take too many pictures in Hat Yai mainly because we were just so tired that we didn't think to pull out the camera. We recommend stopping in Hat Yai for a night or two to see the place yourself.
By the way, Hat Yai came to the party for your desire for Pad Krapow Gai. Our first Thai meal in Thailand in 3 years. To see how to make this delicious meal of chicken stir fried with basil, chilli and garlic, (click here for Pad Krapow Gai recipe).
One last thing, McDonalds in Hat Yai, has so far been the only place in Malaysia and Thailand (thus far) that does not have free wifi. Near the McDonalds, is a couple of cafes that you could sit in and use their wifi. This area is also where you can get a semi decent massage. Enjoy!