Ash Wednesday might be a night for a labyrinth walk that, for the most part, takes the shape of an open walk. Use your normal materials, handouts, guides, etc. Remember, though, Ash Wednesday is an appropriate time for less decorations, starker settings, subdued colors, etc.
Since this would be Ash Wednesday, have a facilitator stand at the entrance of the labyrinth during the walk, with ashes and offer an "imposition of ashes" upon anyone who so desires. In the Christian tradition the ashes often come from the previous year’s Palm Sunday palms that have been dried out and burned. But you can use a variety of ashes; perhaps consider ashes from burning something symbolic in your community that represents impermanence, or a symbol of something which would be helpful to let go of.
Before the actual walk begins, you can tell gathered participants that if they would like to receive the ashes on their forehead, they can turn and face the facilitator directly at the entrance. Or, if they would like the ashes on the back of their hand, instead of their forehead, they may raise up their hand (palm down) as they face the facilitator. You might have a volunteer handing out a very short instruction sheet to those who arrive later.
As the facilitator imposes the ashes, the facilitator might offer words like:
From the ashes of this world you were born to journey with God.
Eventually from the gift that is your life,
So will you return to the the ashes of this world.
Now, as you receive these ashes tonight,
may you be reminded that
however many or few years available to each of us,
Life is short and we do not have too much time
To bring joy to the hearts of those who travel this way with us.
So be swift to love!
Make haste to be kind.
In the gifts of grace and peace
which G_d offers to all of Gd's children.
The last bit of this offering of words is a modified version of a quote from Henri-Frédéric Amiel, 1821-1881. This may seem like a lot to say to each person at the beginning of their walk, but there is usually time to hold people at the entrance in order to spread them out during their walks. Thus, my hunch is that such can work well by using these words for each person as ashes are offered.
Another option would be to use two facilitators at the labyrinth’s entrance -- One imposing the ashes, while the other reads the words above from a small card.