In Section 2, we present horizons, ergospheres, and ergoregions. Section 3 is devoted to basic physical properties of regular interiors.
Ergoregions are defined by [g.sub.tt] < 0 which makes possible extraction of rotational energy (see, e.g.,  and references therein).
There are four cases for the existence of ergospheres and ergoregions shown in Figure 2.
In the black hole case, ergospheres and ergoregions exist for any density profile (the curve (3a) for the case of two horizons and the curve (3b) for the double-horizon case).
Geometry of the rotating black holes and solitons includes ergoregions where processes of extraction of rotational energy can occur which can explain energetic activity of a wide class of cosmic objects.