There’s a staircase leading underground just off the actual mound; descend it. Clear the pile of rubble and inspect the wall behind it. Go through the secret door and stand on the panel. Enter the unlocked door. You can clear the rubble for some loot, and grab the Ancient Coins in this room before standing on the foot panel. A hole will appear in the wall in front of you, so inspect it to unlock the door to your left. Enter the door.
Clear the piles of rubble and collect the heart keystone and treasure. Inspect the wall with the half-circle carpet in front of it to find another hidden door. Grab the treasure from the room behind it and then use the keystone and go through the unlocked door. Pull the furthest statue on the left onto the panel, and enter the newly unlocked door. Grab the Ancient Coins and inspect the hole in the wall to open up a shortcut back out; that will make it easier to backtrack later. Pull a statue onto the visible panel on the floor. Another panel will reveal itself across the room; pull the other statue onto it, and then stand on the foot panel. A staircase will open in the floor. Go downstairs.