Sometime in the not-so-distant future, visitors to Istanbul will be able to soar above the Bosphorus, crossing the famous strait on a intercontinental aerial tramway, the city’s mayor, Kadir Topbaş, announced last month.

With Istanbul in the throes of a building boom, it’s not the only seemingly fanciful idea that’s been floated recently by a public official. During the 2011 election season, Turkish Prime Minister Recep Tayyip Erdoğan unveiled his self-described "crazy project" to build a second, man-made strait parallel to the Bosphorus.

Neither idea has yet reached the actual planning stage, but there's at least one reason not to doubt them: Both Topbaş’s cable car and Erdoğan’s canal were first envisioned by architects and engineers in Ottoman times, along with other equally ambitious building projects­—some of which have actually been carried out.

A book released in Turkish last year, historian Turan Şahin’s The Crazy Projects of the Ottoman Empire, describes some three dozen building schemes of the era, most dating from the 19th century and early 20th century, a period when various sultans sought to transform Istanbul into a Western-style capital.