Anish Kapoor is an artist that I've only in the last few years become familiar with. He is known mostly for his sculptures which engage viewers through their size and simplicity. The sculptures often have an element of mystery and the viewer is able to explore the sculpture by walking in and around it. His use of space and its interaction with the viewer is extremely unique and I think you'd be hard pressed to find an artist who allows as much interaction with their work as he does.
The other thing about his work is that he engages viewers through the materials he uses. I know for me, when things are shiny or have a mystery to their surface, I really want to reach out and touch them. And this is how he creates another level of fascination in his work. Take this piece for example in the permanent collection of the Tate Modern called Ishi's Light.
How badly do you want to walk in ther and touch that shiny dark surface! I can only imagine what it feels like to stand within that sculpture.One of his pieces I feel privileged to see frequently is is Cloud Gate.