Step 3 - Adjusting the Left Wall

The wall is too bright again. You'll fix it now. Add new adjustment layer Levels above the LEFT BEND. Set the Input Levels as it is shown below and create Clipping mask from this layer.

As you can see there is one really dark area because of the adjustment you've just done.

To fix it grab the Brush Tool (B), select some soft round brush and pick the black color. Now click on the thumbnail of the Levels layer and start painting over the circled area. The adjustment becomes invisible.

Step 4 - Adjusting the Right Wall

The right part of the wall should be darker too. Add new adjustment layer Levels above the layer RIGHT BEND and set is as shown below.

Create Clipping mask from the layer. You may notice that the adjustment layer adjust also bottom part of the wall.

You need to hide the adjustment from this part because we will take care about the bottom part in next step and it would not work if one part is darker than another. You hide the adjustment same way as in the previous step. Grab the Brush Tool (B), select soft round brush, pick the black color, click on the thumbnail of the adjustment layer you've just added and paint over the areas you want to make lighter.

Step 5 - Adjusting the Bottom Part

The bottom part is still too bright. To fix it add new adjustment layer Levels and set it as on the picture below.

Grab the Gradient Tool (G), pick the black color and fill the thumbnail of the layer. Then grab the Brush Tool (B), pick white color and paint over the areas of the bottom part of the wall to make there the adjustment visible. Your image should look like the one below so far.

Step 6 - Retouching of Vertical Lines

As you can see on the picture above it's necessary to blend parts of the wall correctly. There are three main parts which need to be fixed - vertical lines, horizontal lines and the stone itself. To do that you will use Stamp Tool (S). If you're not familiar with this tool I would recommend you to take a look e.g. at this video tutorial or write "stamp tool" in google or youtube and you'll find tons more. It's a really powerful tool in Photoshop and it's a pity to don't use it.