This is a red border Kodachrome slide depicting a group at a beach. I don’t know the date, but the swimwear suggests the 1950s as does the slide mount.
Normally, Kodachrome slides keep their colour very well, but this particular example looks quite muted and in fact seems to have some colour shift.
Like the date, the location is unknown and there are not too many clues in the picture to work it out. The beach is pebbled and there seems to be a wall or building in the background with people sitting on it, but it would be difficult for anyone to pin the location down from that information, or the sight of hills in the background. I suspect it is in the UK, but it is also possible that it is the US or possibly a European beach.
The long shadows in the picture suggest either morning or evening as the time of day.