Ribeiro, André TomásRebelo, Ana RitaNóbrega, RuiJorge, Joaquim A.Sakata, Nobuchika2025-11-262025-11-262025978-3-03868-278-31727-530Xhttps://doi.org/10.2312/egve.20251358https://diglib.eg.org/handle/10.2312/egve20251358Natural locomotion in Virtual Reality (VR) is often constrained by the size of the physical tracking space. Portals - virtual connections between distant locations - offer a promising solution to support natural walking in limited physical areas. However, traditional portal implementations often introduce usability challenges, such as requiring large clearances from walls to prevent physical collisions, or creating unnatural transitions between spaces. In this paper, we explore four portal designs for enabling natural walking in impossible spaces: (1) Traditional Portal with a spatial preview and offset from walls; (2) Movable Portal that initially appears on a wall and can be repositioned by the user; (3) Interactive Door: a door-shaped portal embedded in the wall that can be opened interactively; (4) Revolving Door: a portal offering a continuous transition between rooms through a circular motion. These designs emerged from initial user trials that revealed the desire for more flexible and natural transitions between rooms. We conducted a user study (N=31) to evaluate these four portal types, focusing on usability, spatial understanding, immersion, and perceived naturalness. Results suggest that the alternative designs addressed the portal limitations successfully and helped convey a continuous sense of space, with each portal design revealing their strong suits. Movable Portals were commended for their sense of control, Interactive Doors for their naturalness and ease-of-use and Revolving Doors for the best feel of a continuous space, with Traditional Portals being the most preferred for their high ease-of-use.Attribution 4.0 International LicenseCCS Concepts: Human-centered computing → Virtual reality; Interaction techniques; HCI design and evaluation methodsHuman centered computing → Virtual realityInteraction techniquesHCI design and evaluation methods10.2312/egve.2025135810 pages