map.cls

new Map<String,Object>{
  'isBooleanType' => true,
  'integerType' => 42,
  'strings' => 'are stringy',
  'this is where it gets tripy' => new Map<String,Object>{
    'down the rabbit hole' => true,
    'through the looking glass' => new Map<String,Object>{
      'isThisEnoughToGetThePointAcross' => true
    }
  },
}

result.json

{
   "integerType":42,
   "this is where it gets tripy":{
      "through the looking glass":{
         "isThisEnoughToGetThePointAcross":true
      },
      "down the rabbit hole":true
   },
   "strings":"are stringy",
   "isBooleanType":true
}