Hi Trish,
There are 'loads' of caves in Mallorca, and without a guide you'd have problems finding them.
However, one that I'd heartily recommend is 'Cova de na Mitjama', which is in the north-east of the island. This is in low cliffs at the seaside, and is accessed via an inviting-looking tube-like passage, maybe 1.5 m in diameter. Just inside there's a short pitch of ~5?6 m, which often has a fixed ladder; when we went the ladder was very rickety, and bent in the middle. So ? there may or may not be a ladder. If you're taking vertical stuff with you, this won't be a problem, I guess, but if you're combining a 'normal' holiday with a bit of caving, and are travelling light, then it could be an issue.
Anyway, assuming that you can get down the picth, at the bottom you'll find a network of easy, but very well decorated, passages, including a chamber with an underwater connection to the sea, and a shallow salt-water lake.
I'll dig out directions for getting there and PM you.
To whet your appetite: