360-degree video contains a full field of environmental content. However, browsing these videos, either on screens or through head-mounted displays (HMDs), users consume only a subset of the full field of view per a natural viewing experience. This causes a search problem when a region-of-interest (ROI) in a video is outside of the current field of view (FOV) on the screen, or users may search for non-existing ROIs. We propose Outside-In, a visualization technique which reintroduces off-screen regions-of-interest (ROIs) into the main screen as spatial picture-in-picture (PIP) previews. The geometry of the preview windows further encodes a ROI's relative location vis-a-vis the main screen view, allowing for effective navigation. In an 18-participant study, we compare Outside-In with traditional arrow-based guidance within three types of 360-degree video. Results show that Outside-In outperforms in regard to understanding spatial relationship, the storyline of the content and overall preference. Two applications are demonstrated for use with Outside-In in 360-degree video navigation with touchscreens, and live telepresence.