A bottle garden is a small, terrarium-like garden that is contained inside a bottle.
Bottle gardens are easy to make in that all they recquired is a decent bottle (glass is best, but plastics will do), dirt, water, plants, and light. Because the bottles are sealed after setup, the moisture inside doesn't evaporate; it condenses on the side of the glass and stays within the system for continual use. Because of the confined nature of the garden, nothing inside grows past what it's capable of sustaining, and theoretically the bottle gardens (if properly prepared and sealed) could last indefinitely.
Purportedly the oldest bottle garden belongs to a man named David Latimer who planted the garden in 1960, sealed it off in 1972, and has kept it safe since then. Originally there were four plant species inside, but while the other three have since perished, one Spiderwort plant has continued to thrive decades later.