Quest Room 好像跟 Guest room 不一样，Quest room 可以有更多的用途，不一定是客人用，也可以自己用。所以有 ‘要求’ request 的含义。

Quest room ＝ 主人房 Master bedroom 以外的 spare room 备用房间，可以用来做客房，或其他用途。原文说给祖父母来探访时使用，是一个实例。

例句：（请参见一个美国旅馆的网页，链接在下面）

The President‘s Suite is a wonderfully inviting three-room area with a large bedroom which includes a queen-size bed with soft, cotton sheets, electric fireplace for warmth and romance, a two-person clawfoot tub and sitting area. The second room has a wet bar with sink, fridge, microwave, dishes, glasses, sitting area, and closet. The large private bathroom boasts two sinks and large mirror, two person tub/shower, and its own heating source! The Suite is decorated to reflect the Buffalo Tavern era. It is such an warm and comfortable suite!

Doc offers his guests the use of soft, luxurious Turkish bathrobes while staying at Buffalo Tavern! They are generously fitted and 5-star hotel quality. There will be two robes in each quest room, ready for relaxing!

我也看到有房地产网页（参见最下面链接）提到房子的客厅有 Quest toilet，即在除了主人用的洗手间以外，客厅也多一个厕所供选择。

FACILITIES：
3 BEDROOM WITH ONE LIVING ROOM WITH ’QUEST TOILET‘.

建议翻译为：

备用套房

供参考。