I guess many of us started our interest in gardening with cacti. Despite their obvious drawback of really nasty spines they are so often given to children as first plants. I guess because it’s thought, quite rightly, that these don’t quickly die of neglect. However you can kill them with kindness- too much watering or fertiliser, especially in the darker colder months, will eventually kill most cacti. Mind you, if spotted in time, the top can often be cut away from the rotting roots, dried off and re-rooted. Indeed, to my shame, I have had to ‘rescue’ some of mine several times. The converse, of dessication, is still possible but obviously cacti have evolved to cope with this. Sudden unusually hot sun can scorch them -but more of a danger is condensation and drips. Otherwise cacti are amongst the easiest of plants to tend. Given almost any soil as long as it’s free draining and most are happy. And of course a dry sunny position- there are few shade lovers other than a few tree dwelling forms.
Many cacti are satisfactory plants for years for their simple, pleasing, if spiny, forms, and then one day they surprise you when they produce staggeringly beautiful flowers. Many flower sporadically but some such as the Christmas Zygocactus reliably throw blooms every year and if happy in profusion. (Never move a cactus once the flower buds form or they may drop.) And you do not even need a heated glasshouse to get started as many cacti are almost or even actually hardy. It is damp that gets them not dry cold so a cold greenhouse or even an alpine house is fine. Opuntias, somewhat amazingly, are often grown outdoors- I had several at the sunny base of a hedge for several years until rather unexpectedly a plague of slugs not the weather got them.
If you have a sunny warm greenhouse Opuntia species can be so happy they not only flower but fruit- with Prickly Pears. These are spiny outside but sweet inside and rather acid with small seeds, which if you are patient can be sown and raised. (The Dragon fruit and the Pithaya sold in supermarkets are from other, more succulent, cacti and can also be grown from their tiny black seeds embedded in the flesh.) And if you fancy cacti but not those spines there are even some spine-free ones to try such as Astrophytums and the legendary supposedly psychedelic Lophophora williamsi.