The first step is to decide just how much precision you need. Although you could index all geo-points with the default full 12 levels of precision, do you really need to be accurate to within a few centimeters? You can save yourself a lot of space in the index by reducing your precision requirements to something more realistic, such as 1km:

PUT /attractions
{
  "mappings": {
    "restaurant": {
      "properties": {
        "name": {
          "type": "string"
        },
        "location": {
          "type":               "geo_point",
          "geohash_prefix":     true, 
          "geohash_precision":  "1km" 
        }
      }
    }
  }
}

With this mapping in place, geohash prefixes of lengths 1 to 7 will be indexed, providing geohashes accurate to about 150 meters.