The Astronomical Clock, mounted on the south wall of the Old Town Hall in Prague, is a remarkable feat of engineering. Nestled in ornate Gothic decoration, this steampunk predecessor still ticks today - and is even the oldest working clock of its kind in the world, dating back to the early 15th century.

Moving effigies and a procession of the Twelve Apostles were added to the clock in the 17th century and then again in 1865, respectively. Whenever the hour strikes, the animated procession appears through two automatic windows above the main face of the clock and a skeleton statue rings a bell to signal that time is running out.

On its left, a rapacious miser shakes his head in denial of death; on its right, a Turk is occupied with revelry while ignoring the summons; and, similarly, a masculine caricature of vanity looks in the mirror. A golden rooster, though, crows above them, bringing the promise of another hour of life.

The clock is interesting in that it uses four separate time-telling traditions and displays 24 hours of the day instead of the usual 12 hours. A golden hand circling the clock face illuminates the outermost dial, which displays ancient Bohemian time, which was used by Europeans during the Middle Ages and has black background with gold Arabic digits.

The Astronomical Clock additionally indicates stellar time; in addition to the sun's position in the sky, it also displays the moon and stars' positions. We can determine whether the moon is full, crescent, gibbous, or new by looking at a rotating silver and black lunar orb. A dial corresponding to the stars floats above the clock face and shows where the sun rises and sets against a background of the zodiac signs.

This mechanical wonder is a testament to human ingenuity and our long-standing fascination with modeling the universe mechanistically. After over six centuries, it is still ticking today - which is a great engineering feat.