Save with at least 1 skill point before you enter the Mirage Tower. Use the skill point then enter the mirage tower and die, when you are then prompted to 'Save' say 'No' and you will appear in the Mirage Tower with 1 skill point.
When you have completed Quest 25 in the main storyline the Mirage Tower dungeon will become available. Mirror Tower dungeon has 50 floors with random monsters and is located at the lower right portal of the North Sograt Desert. This feature can be played online with other gamers.