To get the treasure chest in the Cave northwest of Jabu-Jabu’s den, follow these detailed steps:

### Step-by-Step Guide

1. **Reach Jabu-Jabu’s Den**:
– Travel northeast through Hyrule Field and then east from the sandy area to come across Seesyde Village.
– From Seesyde Village, head north and east to find some water, using echoes to navigate the area.
– Make your way to the massive rift on your map to reach Lord Jabu-Jabu’s Den.

2. **Explore Jabu-Jabu’s Den**:
– Inside Jabu-Jabu’s Den, you’ll find Hemi and another River Zora. They mention that the only way to open the door is for the chiefs of the River Clan and Sea Clan to play music together.

3. **Travel to River Zora Village**:
– From Lord Jabu-Jabu’s Den, travel west and north up Zora River to reach River Zora Village.
– In the hut at the far northwest part of the village, you’ll find the River Zora Chief, Dradd. However, before you can make a request, the chief leaves, heading towards Crossflows Plaza to try and calm Lord Jabu-Jabu with his music alone.

4. **Crossflows Plaza**:
– Crossflows Plaza can be found northeast of Seesyde Village. If you travel there now, you’ll find Dradd, but he still won’t listen to you. He just complains about the Sea Zora chief, Kushara.

5. **Return to Jabu-Jabu’s Den**:
– Word immediately reaches the area that Lord Jabu-Jabu is now in Zora Cove. This causes both chiefs to head down to Zora Cove without delay.

6. **Enter the Cave**:
– Enter the cave at the northeast part of the Stilled Upper Zora River. This cave is crucial for progressing through your quest and finding the treasure chest.

7. **Use Bombfish**:
– Inside the cave, you’ll encounter Bombfish. These creatures can be used as a tool by detonating them next to enemies or cracked walls to reveal secrets. You’ll need to use them to break the cracked blocks in the cave.

8. **Navigate Through the Cave**:
– Once you’ve used the Bombfish to break the cracked blocks, navigate through the cave carefully. You’ll need to avoid the Bombfish as they explode, and use air bubbles to rest when needed.

9. **Reach the Treasure Chest**:
– After navigating through the cave, you’ll find a Treasure Chest on top of a high wooden block. However, it may not seem possible to reach it initially. To do so:
– Place a Bombfish under the wooden block.
– Run to the nearby ladder and bind the fish before climbing up so that the fish can also reach the block.
– Your reward for this is a Golden Egg, which will supercharge smoothies when mixed with other ingredients.

10. **Optional: Explore the Upper Zora River Cave**:
– If you have time, explore the Upper Zora River Cave located just below the entrance to the Zora River Village. This cave contains puzzle rooms with a swirling circular river and a Wooden Box floating along it. Completing these puzzles will reward you with a Treasure Chest containing 100 Rupees.

### Summary

To get the treasure chest in the Cave northwest of Jabu-Jabu’s den:
1. Reach Jabu-Jabu’s Den.
2. Explore Jabu-Jabu’s Den and learn about the music requirement.
3. Travel to River Zora Village.
4. Return to Jabu-Jabu’s Den.
5. Enter the cave at the northeast part of the Stilled Upper Zora River.
6. Use Bombfish to break the cracked blocks.
7. Navigate through the cave carefully.
8. Place a Bombfish under the wooden block and bind it before climbing up.
9. Collect your reward, which includes a Golden Egg.

By following these steps, you’ll be able to navigate through the cave and obtain the treasure chest.