Practical skills are one of the core competencies in technology, engineering and the natural sciences. However, the busy curriculum in many universities lacks space and time for the learning-by-doing experience to mature. Therefore, we have designed and implemented a virtual laboratory, LabLife3D, to Second Life, to bridge the gap between theory and practice. To date, we have designed five virtual laboratory exercises in the biological sciences and chemistry there: a virus isolation experiment, a laboratory safety tutorial, organic chemistry simulations on (a) decarboxylation reactions and (b) vacuum distillation, and a molecular biology simulation on identifying a virus with polymerase chain reaction (PCR). This paper presents their design process and outlines their contents. General design objectives in virtual laboratories are also discussed, along with laboratory simulations in Second Life by other groups. All the exercises have been designed in accordance with content-specific learning goals and outcomes, which are discussed. In addition to creation of contents, we have also recently studied the usability of our simulations and conducted a student assessment. Preliminary results of the student assessment are presented. 1 MOTIVATION Three-dimensional (3D) virtual worlds represent recent developments in information technology and they will undoubtedly become significant learning spaces for future student generations, the so-called "Millennials" or "Digital Natives". Evidently, though, virtual worlds have not gained as much attention in university education as have other professional computer applications, the social media or user-generated encyclopaedias. Moreover, 3D worlds are often not recognized as a specific entity. Rather, they are often referred to as only a part of elearning, which has caused some of the interest in the more exciting applications of 3D virtual worlds to stagnate. 3D virtual worlds and other virtual learning spaces are best understood as an alternative, not a replacement, to face-to-face communication and traditional teaching methods. They have many significant advantages compared to solely real-life learning spaces, some of which include the following: 1. Virtual worlds are extremely flexible, allowing