The phrase "a landmark night" is correct and usable in written English.
It can be used to describe a significant or memorable evening, often in the context of an event or occasion that has great importance.
Example: "The concert was a landmark night in the history of the music festival, drawing record crowds and featuring legendary performances."
Alternatives: "a historic night" or "a momentous evening."
Both families had vacation houses in Palm Beach, and they enjoyed a landmark night at the movies there.
The U.F.C. had finally staged U.F.C. 200, a landmark night of mixed martial arts, televised on pay-per-view, which the company had been hyping all year.
If Sunday's Tonys were a landmark night for black actors, the awards ceremony inevitably pointed up the scant Broadway roles for Hispanic, Asian and other actors who are not white or black.
It was a landmark night for Tottenham Hotspur, too, as they broke an English club home attendance with 85,011 watching at Wembley, yet the majority were left disappointed as Monaco emerged with a 2-1 win.
It was a landmark night for LBGT candidates too, with America's first openly gay governor, Jared Polis, elected in Colorado.
A 94th-minute Genoa goal inflicted a first league defeat of the season for Juventus and ruined a landmark night for goalkeeper Gianluigi Buffon.
But tonight, all seems well with the good ship Albion (a long-standing metaphor for the Libertines), playing this London venue for the first time since their landmark night here in 2004.
It all overshadowed another landmark night for Cristiano Ronaldo, whose double strike saw him reach 200 goals for the club in all competitions.
Planned as an antenna for telecommunications and brightly colored in accordance with the time's Aviation Law, the tower's two panoramic observatories are mostly frequented by tourists today; the tower constitutes a clear reference point in the center's chaotic skyline, forming a strong landmark, both night and day.
SENATOR John McCain hosted a landmark fund-raising event the other night.
It was only about 12 hours later, after a chauffeur had received a call from Saudi Arabia telling him to go to the £259-a-night Landmark hotel, that the body was discovered in room 312.
