It activates mask of the woman.
Click on the layer mask of the adjustment layer Levels you've just added (with mask of woman still activated). Grab the Brush Tool (B), set the Opacity on 100% and pick black color. Paint inside the mask to hide the adjustment there.
Below you can see how your image looks so far.
Step 21 - Global Adjustments
Blue and cyan tones would suit better to the atmosphere of this picture. You'll add them in this step.
Let's start with gentle desaturating. Add new adjustment layer Hue/Saturation on the top of all layers and set the value Saturation on -25.
For colder color palette add new adjustment layer Color Balance on the top of all layers and set it as shown below.
Step 22 - Adding Moon
I think that the right part of sky is too empty. That's why you'll add moon there in this step.
Download the stock photo of moon listed in the beginning of this tutorial and drag it into your photo manipulation. Place it on the top of all layers and name it MOON.
To get rid off the black background around grab the Magic Wand (W), select the black part and then simply press Delete on your keyboard to delete it.
To blend the moon even better with the rest of the image change its Blending Mode from Normal to screen.
There also should be some aura around the moon. Add new layer under MOON and name it MOON'S AURA. Grab the Brush Tool (B), select some big soft round brush and lower the Opacity on 15%. Pick some very light cyan or blue color and paint one big dot under the moon to create the aura. Below you can see what I mean.
Your photo manipulation should be similar to the one shown below.
Step 23 - Another Adjustments
Time for another two adjustments - Levels and Curves. Let's start with Levels.
Add new adjustment layer Levels on the top of all layers and set it as shown below.
This kind of adjustment adds much colder color palette and also makes it bit lighter. To bring back the original darkness add new adjustment layer Curves and set the curve similarly as on the following picture.
Step 24 - Local Adjustment
In this step you'll adjust some small areas of the picture to create bigger harmony - you'll make woman's face bit lighter, her sunglasses darker and also add highlights on her coat.
Let's start with lightening her face. Add new adjustment layer Levels and set the Input Levels on 0; 1,00; 213. Fill the layer mask of this layer with black to hide the adjustment and let it reappear by painting over woman's face with white brush.
On the following picture you can see how her face looks before and after adjustment.
It's rather small change but it has big impact on the image. Many times the point of adjustment some image is not to make some drastic, dramatic changes but to play with details to create perfect piece.
To darken woman's sunglasses add new adjustment layer Levels on the top of all layers again and this time set the Input Levels on 0; 0,52; 255. Fill the layer mask with black to hide the adjustment and then let it be visible again on the sunglasses. As usually use the Brush Tool and white color to achieve that.
Below you can compare how the sunglasses looks before and after.