GPS sensors usually are unable to give an accurate position in-house. To my knowledge there is no standard way for in-house navigation. Some term to search for: stereo vision, SLAM, marker detection and computer vision as a general term. These techniques are not possible with an Arduino because of the necessary heavy computation.
If you just need to localize one central point and that point is visible from all possible locations you could use a simpler design with some (IR) light at that point and the robot turning around till the sensor "sees" the light, then heading straight towards it. But this isn't very accurate although you could build a tube to limit the opening angle of the sensor.