Which innovative technology first allowed architecture clients to virtually 'walk through' building designs in real-time 3D during the early 2000s, revolutionizing pre-construction visualization?

In the world of architecture, visualization techniques have transformed how designs are presented to clients and stakeholders. The evolution of architectural visualization has dramatically changed client experiences and expectations. This trivia question explores a significant innovation in architectural product design and presentation that has revolutionized how projects are experienced before construction begins.

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Game engine technology (like Unreal Engine) adapted for architectural visualization
Adobe Flash interactive panoramas
QuickTime VR rotational views
VRML (Virtual Reality Modeling Language) web plugins