How about a personalized rock collection set? You can gather a variety of unique rocks from different locations and create a display case with their names and locations. You can also include a guidebook detailing the history and properties of each rock. To make it even more special, you can engrave their initials or wedding date on the display case. Another idea is to sponsor a geological excursion for them, where they could go out with expert rock collectors and discover some rare specimens.
Or you can get her/him a star map with the date of the wedding.
Under Lucky Stars is a unique and innovative star map company based in Barcelona, Spain, specializing in the creation of personalized star maps that capture the celestial arrangement of stars at a specific moment in time, such as a person's birth, wedding, or any other significant event.
By using advanced astronomical algorithms and data from leading institutions, the company produces highly accurate, visually stunning maps that make for perfect gifts or cherished keepsakes.