Portals are magic teleportation devices that allow a user to leave one hex and enter another instantly. They may be an example of Hat Magic. Portals take the form of glowing doorways, and vary in color.LIAB_57:12
The only known portals connect to the Magic Kingdom. Reportedly, one exists in each side's capital. Cities definitely known to have portals are Gobwin Knob (green), Spacerock (blue), and the City of Unaroyal (before its fall). Other capitals such as Transylvito and Faq would also have them, but those have not yet been seen in the comic.
Passing through a portal does not follow the known Movement rules. It apparently does not require movement points, as proven when Parson was able to use a portal despite being a garrison unit with zero move. Further, units may pass through the portal when it is not their turn, because Parson and his casters leave Gobwin Knob during the Royal Crown Coalition's turn, and return during the night (between turns). Erf-b1-p136
As noted above, non-casters are disbanded when they enter a portal. However, Parson was able to pass through without disbanding, and arrive in the Magic Kingdom. A definitive reason for this has not yet been presented. Janis stated that Parson was actually a Hippiemancer, which may or may not be correct. Some other possibilities are: the portal could not see Parson's stats and therefore did not "know" he was a non-caster; the Mathamancy Bracer makes its wearer count as a Mathamancer; Parson as a non-native of Erf is immune to disbanding; or, contrary to what everyone believes, portals don't really automatically disband non-casters. (This last would beg the question of what happened to Queen Bea when she attempted suicide by portal.)