《海底兩萬哩》（日語：ふしぎの海のナディア，英語：Nadia: The Secret of Blue Water）是由南夢宮（Namco）開發並發行的一款日本冒險遊戲，於1991年3月19日在日本的Mega Drive平台上推出。遊戲改編自同名人氣動畫，玩家可以透過遊戲重溫動畫世界，但故事線在某些情節上有所變化，使得遊戲呈現出不同於動畫的新體驗。遊戲共有六章章節，雖然主要沿襲原作劇情，但角色的出場順序及重大事件，如瑪麗（Marie）、怪人加高伊（Gargoyle）、Neo皇帝，以及高潮劇情，都有相當大幅度的改編，給熟悉動畫的玩家帶來新鮮感與驚喜。

遊戲採用俯視2D視角，類似於點擊式冒險遊戲的玩法。玩家操作主角少年Jean，必須透過與NPC對話、收集道具來解謎和推進劇情，而遊戲中完全沒有戰鬥系統，重點放在探索與策略思考。每章節開始時，遊戲提供密碼系統，讓玩家能從該章節起重新開始，方便玩家逐步完成整個故事。遊戲的背景設定在19世紀末，玩家隨著Jean的視角，逐步揭開神秘少女Nadia及其寶石「Blue Water」所引發的一連串事件。從海上探險到敵方陰謀，遊戲完整呈現出冒險故事的張力與懸疑感。

在系統設計上，延續南夢宮對冒險遊戲的成熟理解，界面簡潔，操作直覺，只需上下左右移動並互動，即可完成大部分探索任務。道具收集、謎題解鎖以及角色對話選擇都對遊戲進程具有關鍵影響，玩家必須細心觀察、聆聽角色提示並合理安排道具使用順序，才能順利通關。這種玩法在當時的家用主機市場上，尤其是以戰鬥為核心的RPG或動作遊戲占主流的背景下，顯得十分特別，提供了別具風格的冒險體驗。

市場評價方面，這款遊戲主要受到動畫粉絲的關注與喜愛。由於劇情對動畫進行改編，熟悉原作的玩家能夠體驗到不同的故事展開與角色互動，使遊戲具有一定的收藏與遊玩價值。此外，密碼系統方便分段遊玩，以及無戰鬥設計降低了操作難度，使得冒險焦點更加明確，適合喜歡解謎和劇情探索的玩家。雖然只在日本發行，但憑藉動畫原作的人氣和南夢宮穩定的遊戲製作水準，至今仍被視為Mega Drive時代經典的冒險遊戲之一，也是動畫改編遊戲的代表作之一。其對角色互動、場景設計與故事演繹的專注，即使在缺乏戰鬥元素的情況下，也能感受到完整的沉浸式冒險體驗。

Nadia: The Secret of Blue Water (Japanese: ふしぎの海のナディア) is a Japanese adventure game developed and published by Namco, released for the Sega Genesis in Japan on March 19, 1991. The game is based on the popular anime of the same name, allowing players to experience the world of the series, but with notable deviations in the storyline that create a fresh experience. The game is divided into six chapters, and while it generally follows the original plot, the introductions of characters such as Marie, Gargoyle, Emperor Neo, and the climactic events are significantly altered, offering surprises even for players familiar with the anime.

The gameplay uses a top-down 2D perspective, resembling a point-and-click adventure. Players control the protagonist, a young boy named Jean, and must interact with NPCs and collect items to solve puzzles and progress through the story. There is no combat system; the focus is entirely on exploration and strategy. Each chapter begins with a password system, allowing players to resume from the start of that chapter, which facilitates gradual completion of the story. Set in the late 19th century, players follow Jean as he becomes entangled with the mysterious girl Nadia and the enigmatic jewel, the Blue Water, uncovering conspiracies and embarking on adventures across land and sea.

From a design perspective, Nadia: The Secret of Blue Water reflects Namco’s expertise in adventure games. The interface is simple, and controls are intuitive, allowing players to move in four directions and interact seamlessly with the environment. Item collection, puzzle-solving, and dialogue choices have a direct impact on the game’s progression, requiring careful observation and planning to advance. In a gaming landscape dominated by combat-oriented RPGs and action titles, this focus on story and exploration provided a distinctive and engaging adventure experience.

In terms of reception, the game was primarily appreciated by fans of the anime. Its storyline deviations offered new interactions and unexpected plot developments, enhancing both its collectible and replay value. The password system made it easier to play in stages, and the lack of combat lowered the entry barrier, emphasizing puzzle-solving and narrative engagement. Although it was released only in Japan, the game’s connection to a popular anime franchise, combined with Namco’s reliable production quality, has cemented its reputation as a classic Sega Genesis adventure title. Its attention to character interaction, scene design, and storytelling allows players to enjoy a fully immersive experience despite the absence of combat mechanics, making it a memorable example of anime-based adventure games.