There are natural sand dunes in typical places such as beaches and near lake beds, to which many people enjoy climbing up on the sand dunes and then enjoying a nice ride back down the sand dunes' face. Then too there are manufactured sand dunes made by companies that need to utilize sand for construction purposes, mortar, and so forth. In general, sand dunes are stable, but that stability is based upon the underlying makeup of the materials of that sand dune, its density, its construction, and its form, which often fails to take into account the potential of either visible sink holes or the creation of hidden ones.
The thing about sand dunes that presents a potential danger is the illusion that a sand dune will often give people, which is that it is inherently stable, when in fact, natural sand dunes are forever changing by weather, by age, in visible and invisible ways that are not necessarily seen or recognized and because of those changes, there are often areas of the sand dune that aren't as stable as other parts of the dune which creates the real potential for there to be a problematic sinkhole in the sand dune itself.
The obvious problem of a sinkhole is the fact that it can kill you, via suffocation, as a sand dune does not construct itself in a way that you are able to easily step your way out of it, should you sink significantly below the surface. This again demonstrates the mirage that things that we take for granted as being solid, for everyday activities and enjoyment, may not be as secure as we might imagine.
Then again there is another type of sand dune, created by industrial machines that often create wonderfully high piles of sand for the construction of buildings and other infrastructure, to which sand is a material that is used in the mixing in and the creation of concrete and asphalt. These manmade sand dunes are typically fenced off from the general public as they are often on company construction property, but not always. For instance, there are times when huge sand dunes are dumped and then left at a given construction site, so that those manufacturing cement or the like can utilize them on a given project.
Not too surprisingly, children especially are attracted to playing in the sand, and there are times when despite whatever fencing or security or signs that may be displayed at a given workman's site the urge to play takes control over proper discretion and the lure of fun with a manufactured sand dune for the adventurous is too strong. In most instances, this may well just be a rite of passage, but not all sand is the same, some sand is much softer than others, and sand with more give in it, naturally or in conjunction with wet weather, can result in the creation of a sinkhole with devastating consequences.
It is wise to remember that sand is always shifting, seldom completely stable, and thereby caution should always be a careful consideration.