"砂上の樓閣" meaning in Japanese

{
  "lang": "Japanese",
  "lang_code": "ja",
  "pos": "soft-redirect",
  "redirects": [
    "砂上の楼閣"
  ],
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Japanese terms read with on'yomi",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Japanese terms with non-redundant non-automated sortkeys",
          "parents": [],
          "source": "w"
        }
      ],
      "id": "en-砂上の樓閣-ja-soft-redirect-47DEQpj8",
      "tags": [
        "no-gloss"
      ]
    }
  ],
  "word": "砂上の樓閣"
}

{
  "lang": "Japanese",
  "lang_code": "ja",
  "pos": "soft-redirect",
  "redirects": [
    "砂上の楼閣"
  ],
  "senses": [
    {
      "categories": [
        "Japanese terms read with on'yomi",
        "Japanese terms spelled with 上 read as じょう",
        "Japanese terms spelled with 樓 read as ろう",
        "Japanese terms spelled with 砂 read as さ",
        "Japanese terms spelled with 閣 read as かく",
        "Japanese terms with non-redundant non-automated sortkeys"
      ],
      "tags": [
        "no-gloss"
      ]
    }
  ],
  "word": "砂上の樓閣"
}