If you missed the MAZE area and EASTERN SHAFT KEY, you can backtrack from the next level, INSIDE THE GREAT PYRAMID, to continue exploring in KHUFU'S QUEEN'S PYRAMIDS.
Start by exiting the pyramid onto the ledge with the keyhole where you used the GUARD'S KEYS.
Step down onto the flat ledge below and to the left of the doorway. This ledge is 3 tiles wide. Take a standing jump from about the middle of the leftmost tile down to the flat area on the tier below, which is also 3 tiles wide.
Follow this flat ledge nearly to the end. Take a standing jump from about the middle of the leftmost tile to the flat below on the left. ahead and below.
Now, either step back from the edge and take a standing jump down to the flat ledge two tiers down and one tile to the left (white arrows), or step onto the slope to the left and slide down to land on that same flat ledge (blue arrows). Then step off the edge to land on the block jutting out above the excavation pit.
Turn left, take a few steps back from the edge, then take a standing jump down to the next block ledge.
From there, take a running jump to the next, slightly higher block.
Turn right (west) and take a running jump across the pit to the area where you'll find a movable block and the entrance to the MAZE. Follow the main walkthrough starting with the PYRAMID ENTRANCE section.