All buildings begin as ideas - but not all make it off the page. Some of the most visionary architectural designs have been shelved due to financial constraints, political hurdles, or the untimely demise of key supporters. These unrealized dreams form a lost library of architectural wonders, offering glimpses into how our world might have looked.

This concept inspired Los Angeles-based writers Sam Lubell and Greg Goldin to pen the book "Atlas of Never Built Architecture." In their introduction, they reflect on the ephemeral nature of architectural ambition: "As we unearthed each treasure, shaking off the dust clouds of memory and the inscrutability of faded ink, we were reminded that our reality is far less fixed than we think. Every decision could have resulted in something different."

Lubell and Goldin compiled sketches and stories of over 300 unrealized structures, ranging from skyscrapers and hotels to casinos, government buildings, cemeteries, and even a "floating theater boat that resembles a UFO." These proposed structures span more than a century and cover 80 countries. Here are five notable designs that were proposed for various sites worldwide, along with what currently stands in their intended locations:

1. The Proposed Xanadu Hotel for the Las Vegas Strip

In 1975, the Xanadu Corporation envisioned a new hotel on the Las Vegas Strip inspired by the mythical Himalayan paradise of Shangri-La. The Xanadu Hotel's design featured a circular bar suspended in the air, seemingly floating thanks to hidden columns. Despite approval from Las Vegas authorities, the project was halted due to disputes over utilities and sewer lines. The site intended for Xanadu is now occupied by the Excalibur Hotel & Casino. Opening in 1990, this medieval-themed property was once the largest hotel in the world, offering a stark contrast to the futuristic vision of Xanadu.

2. Finance Place in Manhattan

In 1961, real-estate developer William Zeckendorf acquired Manhattan's historic Singer Tower with plans to replace it with a new home for the New York Stock Exchange. The proposed 45-story Finance Place, designed by Pei Cobb Freed & Partners, resembled a "beautifully tapered Mayan temple" with a massive column-free trading floor. Today, One Liberty Plaza occupies the site. This 54-story building houses tenants such as law firm Cleary Gottlieb Steen & Hamilton and the New York City Economic Development Corporation.

3. Peruri 88 in Jakarta

The Peruri 88 project proposed a complex of Tetris-like structures in Jakarta, featuring spaces for offices, townhouses, a luxury hotel, movie theaters, a wedding chapel, and a mosque. The design included escalators spanning 15 stories, creating a vertical cityscape. Despite its ambitious design, Peruri 88 never materialized, and the site remains undeveloped land, a blank canvas in the heart of Jakarta.

4. The Zaha Hadid Opera House in Dubai

Renowned architect Zaha Hadid designed a futuristic opera house for Dubai, featuring sweeping, organic forms that seemed to defy gravity. The design promised to transform Dubai's cultural landscape, but financial issues and shifting priorities led to the project's cancellation. In its place stands the Dubai Opera, a more conventional yet impressive structure shaped like a dhow, reflecting the region's maritime history. It has become a cultural landmark, hosting a variety of performances.

5. The Chicago Spire

Proposed by architect Santiago Calatrava, the Chicago Spire was set to be the tallest building in the Western Hemisphere, with a spiraling design reaching 2,000 feet into the sky. However, the 2008 financial crisis halted construction, leaving a deep hole in the ground. The site of the Chicago Spire is now a park and open space, serving as a reminder of the ambitious project that could have reshaped Chicago's skyline.

These unrealized buildings remind us of the fluid nature of architectural dreams. While some visions remain on paper, the spaces they were meant to fill continue to evolve, telling new stories with each transformation.