All of the tomb chambers of the great pyramid have been explored. However, there are still some parts that aren't fully known such as the small "air shafts" that come out of the king's chamber and queen's chamber. Robots have been sent into these, at the end are limestone doors. I believe some of them also contain hieratic characters, likely some measurements of the shafts. These shafts are unique to the great pyramid are unique and their exact purpose is still unknown, although a number of hypotheses do exist.

Another part of the pyramid that has not yet been explored is a series of internal ramps that were used to construct it. It is debated whether these ramps actually exist or not, but at least some intriguing evidence has been found to support the theory. For example, a micro gravimetric analysis of the structure that was conducted in the 1980s contains an image of the pyramid with what appears to be the remains of a spiraling ramp inside. These ramps, if present, would have been used for construction and thus unlikely to contain many artifacts. This theory comes from the architect Jean-Pierre Houdin and is described in the book "The Secret of the Great Pyramid" (2011) that he coauthored with the Egyptologist Bob Brier "

Here is a 3d model of the pyramid that you can look at: http://giza3d.3ds.com/#discover