A huge, fat, spearmint-blue house currently sits in the courtyard of the Museo dArte Contemporanea Roma (MACRO), which is exhibiting work by installation artists Erwin Wurm and Leandro Erlich. Puffy, life-size and spreading, the house fills the space between the museum's modern glass facades and overhead walkways as if it has fallen out of a cartoon and no-one is quite sure how to send it back. It is almost disappointing when you touch the walls and discover they are not cloud-like, squishy or edible.

Created by the Austrian artist Erwin Wurm (1954-), "Fat House" (2004) is both an illustration of the artists ongoing campaign to reinvent static sculpture as a dynamic, living force and a meditation on the nature of art itself. Inside, the house talks to you in a Woody Allen-esque stream of consciousness that reveals it is suffering from a serious identity crisis. "Am I a house? Am I an artwork?," it asks in an Austrian-American accent, fretting about why it is inside rather than outside, about why it's fat, and about whether people like it or not. "People smile at me," it reasons. "They are friendly. I believe they think I am a nice house. Maybe they think I am a beautiful house." But is it art because it is fat, and if so, it wants to know, are all the overweight people art pieces?

Leandro Erlich (1973-) is a master illusionist from Argentina who requires viewers to interact on a physical and personal level with his work as a matter of course. In this first solo show at an Italian museum, his love of simple, effective trickery and illusory twists to the commonplace is demonstrated by "Broken Glass" (2004), in which the only thing missing from a normal-looking bathroom is the vampire-like absence of your own reflection in the mirror. In "The Staircase", a modern stairwell with tiled floors and a handrail has been turned on its side, so you can walk between the whorled floors but not on them.

But it is with the atmospheric "Doors. Las Puertas" (2004) that Erlich most impresses. You enter a dark room, from which two doors lead out. Bright light streams from under both doors, as if behind them is a sun-beaten garden on a midsummer day. But the moment you choose a door and step through, you find yourself in another dark room with two doors leading off it, the same bright, promising light shining from behind them. Once again, you try a door in search of the light, once again you are disappointed, and so it goes on a minimalist retelling of the choices we make in life and the pervading suspicion that there must be something better happening just over there.

The joy of installation art as tactical, physical and interactive as that of Wurm and Erlich is that it is impossible not to engage with it on some level. Even people usually left cold by modern art will find something in the works of these two artists to challenge, distort or perhaps even affirm their perceptions of reality. For the price of a 1 entry fee, this is not a bad exchange.

Erwin Wurm, until 31 May, and Leandro Erlich, until 7 May.

MACRO, Via Reggio Emilia 54, tel. 06671070400.