diff --git a/exercises/UNIX_HPX_exercise_instructions.md b/exercises/UNIX_HPX_exercise_instructions.md
index 605121b40bca61d6fe3f64dce4cd09b4fe9d9cf5..4f2e92ac47e4aa769cff2a93c2817c60b125ed2d 100644
--- a/exercises/UNIX_HPX_exercise_instructions.md
+++ b/exercises/UNIX_HPX_exercise_instructions.md
@@ -1,4 +1,4 @@
-##Exercise 1 - Navigating the filesystem on command line
+## Exercise 1 - Navigating the filesystem on command line
 
 **Objective:** get familiar with navigating the directory tree and listing
 the content of directories.
@@ -22,3 +22,66 @@ the content of directories.
       same as `ls -l -h -a`.
    * *Note:* some options have both a "short" and a "long" form. E.g. `ls -a`
      is the short form for `ls --all`.
+
+
+<br>
+<details><summary><b>Exercise solution</b></summary>
+<p>
+
+1. Printing the current working directory:
+
+    ```sh
+    pwd
+    ```
+
+2. Navigate to the current directory, or navigate in and out of it.
+
+    ```sh
+    # If you are not already in the practicals directory.
+    # Note: in the command below, you need to replace /path/to/directory/ with
+    #       the actual absolute or relative path of the directory where your
+    #       "practicals" directory is located.
+    cd /path/to/directory/exercises
+    pwd
+
+    # If you are already in the practicals directory.
+    cd ..                # Change to parent directory.
+    pwd                  # 
+    ls -l                #
+    cd exercises/   # Go back into the practicals/ directory.
+    ```
+
+3. The `.` symbol is a shortcut for the current directory. So running `cd .`
+   has no effect since it simply changes to the same directory we are already
+   in.
+
+   The `.` shortcut is useful in some situations. E.g. if you want to copy
+   a file to the current directory you can do `cp /file/to/copy .`, or you
+   can run an executable located in the current directory with `./run_me.sh`.
+
+
+4. Listing the content of the `exercises/` directory with different `ls`
+   options. the effect of the different options is described in the comments
+   of the code block below.
+
+    ```sh
+    ls       # Prints the names of files and directories
+    ls -l    # List content of the subdirectory in "long listing" format. This
+             # provides additional details for each file/directory, such as
+             # its permissions, its size and its last modified date.
+    ls -lh   # Adding the "-h" option displays file sizes in "human readable"
+             # format. The size of files are shown in kB, MB, GB, instead of
+             # their size in bytes (octets).
+    ls -lha  # Adding the "-a" option additionally displays hidden files and
+             # directories. These are files/directories whose name starts with
+             # a dot ".". The "-a" is the 
+             # Hidden files are often used to store program configurations.
+    ```
+
+   **Tip:** It is possible to define a shorthand for longer commands that you use often, a so called `alias`. On Science Cluster, there are already some pre-defined useful aliases, among them `ll` (standing for `ls -lFh`) and `la` (standing for `ls -lA`).
+
+
+
+</p>
+</details>
+<br>
\ No newline at end of file