There are 27 galleries in total, 9 of each type. To play them you will need to first unlock them by getting the appropriate collectible. See "Fill the Pocket" for more info on where to find them. To finish the gallery, you need to have a score recorded. For Survival, that means just continuing until you die, but for Trek that means finishing the map. If you die in Trek, you will not get credit for finishing the level. For Quick Draw, you must reach the maximum required score to get credit for finishing the gallery. See "Hunting for Gold," "Gold all the Way" and "Keep Them Comin'" for more information.