Cryosealing
Cryosealing was a process invented by the Ta-Deth, which altered the cellular structure of a material at the atomic level, essentially preserving inert materials like stone, wood, and metal from oxidation, wear and tear, and other molecular degradation. It did not work on living flesh.
It was the foundation on which the Ta-Deth built their society, and the foundation on which the Cosmpiercers were constructed. Old beyond reckoning, these ancient scanning stations have survived the test of millennia, but thanks to the culture, ethics, and craftsmanship of the Ta-Deth's approach, they remain in good working order - as do many other items of Ta-Deth make.
Unfortunately, the skills used in Ta-Deth craftsmanship are lost to time, unable to be replicated by modern means. Such is the quality of their legacy, however, that there are plentiful amounts of Ta-Deth artifacts still in use today, far more than any other extinct Elder Race. Though the Cosmpiercers are the largest, most visible and famous of these, smaller military bases, settlements, research stations and even ships have been found throughout the galaxy, and there is a brisk trade in Ta-Deth tech among collectors.