A version of Sandys's description appears in Samuel Purchas, Purchas His Pilgrimage: Or Relations of the World and the Religions Obserued in All Ages and Places Discouered, from the Creation vnto this Present Contayning a Theologicall and Geographicall Historie of Asia, Africa, and America, with the Ilands Adiacent, fourth edition (1626):
Full west from Cairo, close vpon the Libyan Desarts, hauing crossed Nilus, and a Playne twelue miles ouer, they came to the three Pyramides, the greatest of them is ascended by two hundred and fiftie fiue steps, each step aboue three feet high, of a breadth proportionable. No stone so little through the whole, as to bee drawne by our carriages, brought out of the Mountaynes of Arabia, with a double wonder of the conueyance and mounting. The North side is most worne by reason of the humiditie of the Northerne winde in these parts. From the top is discerned the Countrey, with her beloued Nile, the Mummes and many huge Pyramides afarre off, each of which, were this away, might be reputed wonderfull.
As Jim remarks in a comment beneath the posted question, Sandys has just ascended the 250 steps of "the greatest" of "the three Pyramides" west of Cairo and is now surveying the desert landscape all around and the Nile in the distance. From his vantage point, he can see many other "huge Pyramides" far in the distance, and he observes that any one of these would be deemed a marvel of construction and engineering if it were not inevitably compared to the even larger pyramid that he stands atop. The phrase "were it away" simply means "were the Great Pyramid not to exist at all—or not to be in proximity to these other pyramids."