In 1916, a Greek businessman and philanthropist named Marinos Korgialenios bequeathed 200,000 drachmai to the National Observatory of Athens. His stated purpose: to fund the purchase of a large equatorial telescope. The director of the Observatory at the time was Demetrios Eginitis, a personal friend of Korgialenios, who had encouraged the gift. What followed was a long delay that reads like a summary of 20th-century Greek history. The First World War postponed any purchase. Then the Greco-Turkish War intervened. After the Second World War, the accumulated inflation and economic devastation had eroded the bequest so severely that the then-director Stavros Plakidis concluded a purchase was impossible. Finally, in 1971 — 55 years after the original gift — Demetrios Kotsakis applied to the Greek government for 12,000,000 drachmai to supplement the long-diminished bequest. The application succeeded. Four years later, in 1975, a 1.2-meter (120 cm) Cassegrain reflector telescope built by Grubb Parsons of Newcastle was installed on a newly established mountaintop site. The Koryialenio telescope, as it is sometimes called, had arrived.

Kryoneri Observatory sits at 930 meters above sea level on Mount Kyllini, in the Corinthia regional unit of the Peloponnese — the closest settlement being the village of Kryoneri, from which the facility takes its name. The main telescope is a Cassegrain reflector: a design that uses a large parabolic primary mirror (1.2 m / 120 cm across, made from Zerodur, the ultra-low-expansion glass ceramic used in precision optics) paired with a smaller hyperbolic secondary mirror (31 cm, also Zerodur) to focus light through a hole in the primary. The mounting system uses a modified torque-tube equatorial design. In 2016, the telescope was converted by DFM Engineering to include a prime focus configuration, adding a Prime Focus Instrument that dramatically widened its field of view — the modification that made it suitable for the NELIOTA project. The observatory campus includes a dome building housing the main telescope, a roll-off building for a second smaller telescope, and support buildings.

From 2017 to 2023, the Kryoneri telescope's main task was watching the Moon. The NELIOTA project — Near-Earth object Lunar Impacts and Optical Transients — was funded by the European Space Agency with a specific scientific goal: determine how often small near-Earth objects hit the lunar surface, and how they are distributed by size. The method was to watch for impact flashes: the brief bright streaks of light produced when a rock traveling tens of kilometers per second strikes the airless lunar surface. For six and a half years, the telescope monitored the Moon's darkened limb, night after night, cataloguing these flashes and calculating from each one the size, mass, and collision temperature of the impacting object. By the time NELIOTA concluded, it had become the most extensive study of asteroid-lunar collisions ever conducted. The results informed calculations of impact risk for Earth, since the Moon and Earth share a similar local debris environment.

The observatory did not stop at the Moon. The European Space Agency's European Space Operations Centre selected Kryoneri as one of its satellite monitoring stations — tasked with tracking orbital movements as part of what the ESA terms planetary security, monitoring the increasingly congested orbital environment around Earth. A sensor array deployed in November 2021 by Cilium Engineering now operates as part of the Very Wide Field of View network, a joint Greek-Polish initiative to detect objects in low Earth orbit using optical triangulation. Kryoneri's was the first of four planned stations to be deployed. Then came the deep space laser. The NASA Deep Space Optical Communications system installed a high-power transmitter at Kryoneri — the only European node in the network — and on 7 July 2025, the beam crossed the void to Psyche. It is a long way from a businessman's 1916 bequest to a laser conversation with a spacecraft orbiting between Mars and Jupiter. But the line connecting them is unbroken.