To the northwest of the pyramid of Sahure, about halfway to the Solar Temple of Userkaf, an unfinished platform for a pyramid has been discovered. If finished, it would have had a base lenght of approximately 100 by 100 metres, making it one of the larger pyramids at Abusir. It is impossible to estimate the height it would have had, since the building activity stopped probably a few weeks after it had been started.
 

View on the Unfinished Pyramid, taken prior to its excavation.
Source: Verner, Abusir, p. 114.

The excavation of the pit that was to house the burial chamber, and perhaps also an antechamber, had already started as well. This unfinished monument is tentatively credited to Shepseskare, an ephemeral king who may have ruled either before Neferefre or between Neferefre and his brother, Niuserre. This tentative identification is based on the assumption that the unfinished pyramid belonged a king of the 5th Dynasty, which leaves Shepseskare and Menkauhor. That it must be a 5th Dynasty pyramid is clear not only from where it was located, but also from the way the works, however incomplete, were done.

Recent research, however, has shown that it is more likely that the tomb of Menkauhor needs to be located in Saqqara rather than Abusir, so Shepseskare remains the only possible king to whom this unfinished pyramid can be credited.

If this is correct, then Shepseskare may not have ruled much longer than a couple of months, if not perhaps even as briefly as a couple of weeks.