I have read that when the shift in consciousness or ascension occurs, there will be actual, visible portals open on Earth that must be entered in order to cross physically into the new dimension. Is this true?

The portals you refer to are those points on the grid encircling the Earth that are intersections of ley lines. These points contain the higher energy that will be required in the new consciousness. The portals will indeed physically open, but they will not be seen; they will be sensed. It is similar to the energy felt as a tingling in arms and legs when they fall asleep. It is important to know that not only will this tingling alert individuals to the points of high energy— that are, frankly, everywhere now— but that each and every person will also be given the opportunity to react to that energy.