These are not exactly altars, but are similar in form! Walking out on Stearns Wharf in Santa Barbara, there were four temporary "installations" whose builders were nowhere in sight. Presumably constructed by the local homeless, passersby read signs inviting them to coin toss (MAKE A WISH) and chip in for a meal (JUST PLAIN HUNGRY). My favorite part was the meal of sand.
One Yelper writes, "Seeing the homeless blankets on the side of it so you can toss change to them is one of the most inventive ways I've seen to collect spare change."