-- an awstruck Hermione viewing the effects of the Bell Jar on a Death Eater (OP35)
This room is filled with beautiful, dancing, diamond-sparkling light. Clocks can be found on every surface, “large and small, grandfather and carriage, hanging in spaces between the bookcases or standing on desks ranging the length of the room, so that a busy, relentless ticking fill[s] the place like thousands of minuscule, marching footsteps (OP34).” A huge crystal bell jar stands at the far end of the room, and it is from this that the sparkling light comes. The bell jar stands on a desk and appears to be full of a billowing, glittering wind. Inside the jar, rising and falling on the glittering current, a tiny object moves through an endless loop. The object is a small hummingbird, but it isn’t always a bird. At the bottom of its circuit, the bird is within its egg. As it rises, it hatches and grows into a mature bird by the time it reaches the apex of its path. On the way back down, it becomes a fledgling bird and then re-enters its egg, which reforms around it. This progression of time repeats over and over within the jar. A large glass-fronted case stands against a wall within which many Time-Turners of various sizes rest on shelves.
The path through this room, toward the bell jar, is a narrow passage between the many desks. At the far end, where the Time-Turners are located, is another door which pushes to open.
Notes and interesting facts
The Ministry of Magic's entire stock of Time-Turners was destroyed during the Battle of the Department of Mysteries (OP35). There were, however, several others in private hands and one of these was used to nullify a second prophecy about Lord Voldemort's return (CC4).
From the Web
Writing by J K Rowling on WizardingWorld (Pottermore): Time-Turner
Harry Potter Wiki: Department of Mysteries
WizardingWorld (Pottermore) feature: The most mysterious things in the Department of Mysteries