Developing virtual worlds using toolkits and conventional programming-based approaches is a tedious, time-consuming, and often frustrating task. Too much learning of the toolkits and the basic development technology is necessary before the development can start. Even after that, it takes a long time to develop, test, and modify virtual worlds. At ISS, we are following a highly interactive and visual approach to virtual world construction, which allows virtual world designers to work with high-level concepts. This approach facilitates exploration in design and rapid prototyping. To achieve our goal, we are focusing on the following four base technologies: Bricks, a toolkit to support the development of virtual worlds; WorldNet, a toolkit to support the development of network-based virtual worlds; VizNet, a system that helps visualize a large collection of objects; and the Virtual Workbench, a crafting environment that uses virtual reality to build and manage objects.