There is an Indian restaurant in the middle of Linz that serves authentic Indian food: Royal Bombay Palace. I really enjoy hot and spicy meals and I’m one of those people ordering everything extra hot.
Try it, it’s the best Indian Restaurant around.
If you like your meal very hot just order a glass of salted (or mango) Lassi, it mitigates the effect and let’s you eat all extra hot. Here is the menu card (PDF), I recommend the ‘Chili Chicken’ if you like meat!
We arrived there at 22:30 after a whole day of hard work and got something to eat despite the fact that they close at 23:00. Excellent service and great food, this is rare in Linz!