Whilst it's a single person game (although you can apparently play co-op),
you control a party of three, each of them with their own special ability.
You have to choose your three explorers from seven available at the very start
(the twins count as one character) and off you go.

Each of the characters has a special ability, which will likely be useful generally
but will be necessary to utilise in the character specific areas. The game consists
of a number of common areas, which you will traverse regardless of who you
choose as part of your team, and then an area for each of the seven characters.
Who is in your team will determine which of those areas you have to traverse,
and the special ability will be a necessary part of successfully doing that.

Find out more it flotsam's review of

******** The Cave ********