Hiding Your Altar
For some of us, it's just not practical or allowable to have an elaborate and permanent altar in our homes. If you are in the broom closet, then it's likely your altar needs to be too.
A temporary altar
Your sacred space need not be in a permanent location. If you have special items that you like to use for ritual, you can simply store them in a safe place out of sight. You can bring them out and set up your altar whenever and wherever you are able. You might even consider taking them outside to a secluded place if it's too awkward to do so at home.
Hide in plain sight
You'd be surprised how easy it is to have a permanent altar area without attracting any attention. You don't need to be overtly Pagan with the items you choose. A huge chalice with a pentacle engraved on it isn't the only way to represent Water. You could use seashells or a pretty flower vase instead. A feather could represent Air, and an interesting stone for Earth. I do love candles for Fire, and they are such common items that I doubt anyone would question them.
A few carefully thought-out knick-knacks can represent the elements as well as the God and Goddess, and nobody need be the wiser.
Think vertically
This is just another way to hide your altar in plain sight, one that works particularly well if you are short of space. Your altar doesn't need to be on a shelf or table top. Use the walls. Hang non-Pagan artwork that represents the things you would like to have on your altar. A bulletin board would also work, especially if you are living at school in a dorm room. You won't be able to use these 'items' like you would physical items on an altar, but images can be powerful reminders of your spiritual path.
Don't forget: having an altar is important, but not a requirement. If you are always going to be stressing over having your items found or getting caught, your mind will never be clear enough for meaningful rituals anyway. Going without an altar altogether is always an option.
