The open cluster NGC 6253, which looks like a loose gravitationally-bound collection of yellow and red stars, is located at a distance of roughly 5900 light years (1.8 kpc) from Earth in the constellation Ara [1], which is supposed to represent an altar [2]. This constellation is sufficiently obscure that I frequently forget that I have actually talked about the constellation before in my podcast, and I would guess that people listening to this podcast series have also forgotten about it. Anyway, NGC 6253 has a series of characteristics that make it somewhat unusual in terms of open clusters, and being in the constellation Ara is not one of those characteristics.
First of all, NGC 6253 is old by open cluster standards. The age of any cluster is determined by looking at which hydrogen-fusing stars are present within the object. Very massive, very bright blue hydrogen-fusing stars will burn through all of the hydrogen in their cores in just a few million years and will explode as supernovae, while Sun-like stars will take 10 billion years to burn through the hydrogen in their cores before becoming red giants and then transforming into planetary nebulae, and red dwarfs will, very plainly, live for extremely long times. NGC 6253, which doesn't contain the very bright blue stars but does contain the Sun-like stars and things somewhat brighter than the Sun as well as red dwarfs, is about 3 billion years old [3], which is quite old as far as open clusters go. Most other open clusters tend to get shredded by the tidal forces of the Milky Way and a few hundred million years or so, so for any open cluster to make it to an age of over 1 billion is quite unusual.
However, NGC 6253's age is not its most unusual characteristic. What makes this cluster especially weird is that the outer atmospheres of the stars within the cluster tend to contain abnormally high amounts of elements heavier than hydrogen or helium [3, 4, 5, 6]. All hydrogen-fusing stars, including the Sun, are not just balls of pure hydrogen with small amounts of helium in their cores. Instead, they contain small amounts of other elements that were drifting around in the interstellar clouds of gas that they originally formed from. Some of these heavier elements formed within very massive stars that exploded as supernovae, while other heavy elements formed in the nuclear processes that take place when stars eject their outer gas layers when they reach the ends of their lifespans (either forming supernova explosions or planetary nebulae).
These heavy elements build up in the interstellar medium over time, so stars that formed when our galaxy was younger will contain fewer heavy elements than stars that formed later. However, it's very unusual to see stars with substantially more heavy elements than what the Sun has in its outer atmosphere, and NGC 6253 is one of the very few clusters of stars where this is the case [3, 4, 5, 6]. Notably, the stars contain high amounts of oxygen and iron, which are two elements that astronomers commonly look at to calculatet the overall ratio of heavy elements to hydrogen.
(By the way, astronomers refer to these heavy elements as "metals" and the ratios of these heavy elements to hydrogen as measuring "metallicity", but oxygen and some of the other elements that astronomers call metals are not metals in the sense that most other normal, rational human beings would think, so I have avoided using that term metallicity in my podcast series because it would confuse everyone outside of professional astronomy.)
Anyway, the big question regarding NGC 6253 is why do the stars within the cluster contain such high amounts of these heavy elements in the first place. One notable possibility is that NGC 6253 may have formed closer to the center of the Milky Way. This is an older part of the Milky Way where stars have been forming and dying for a longer period of time and therefore where dying stars have been able to deposit more heavy elements into the interstellar medium. The only problem with this explanation is that NGC 6253 does not necessarily look like it originated from the center of the galaxy [6]. Instead, the orbit of NGC 6253 makes it look like it originated from somewhere in the disk of the Milky Way somewhere a little bit inside the orbit of the Sun but nowhere near the center of the galaxy [6]. Unfortunately, I could not find any science paper providing any other good explanations of why any open cluster might contain abnormally large amounts of heavy elements (or, in confusing professional astronomy terms, why some clusters of stars have extremely high metallicities) if they did not form in the center of the Milky Way, but I assume that people will eventually revisit this question regarding NGC 6253 in future research.