Option A is incorrect. Aksai Chin is located to the east of Ladakh, whereas the Siachen Glacier is situated to the northwest of it.

Option B is incorrect. Leh is located to the south of the Siachen Glacier. The glacier lies in the eastern Karakoram range, far north of Leh.

Option C is incorrect. Gilgit is in the Gilgit-Baltistan region, which is west of the Siachen Glacier. The glacier is not located to the north of Gilgit.

Option D is correct. The Siachen Glacier is located north of the Nubra Valley in the eastern Karakoram range of the Himalayas. It is the world's highest battlefield, where India maintains a military presence.

Hence, option D is the correct answer