Moroni is a coastal town and also the capital of The Comoros. It's a very small capital, which is essentially a port, so you'll see small boats exporting vanilla and coffee. The mosque is the stand out building along the port! There's not a huge amount going on, but this is a great place to people watch both day and night. Also one of the three ATM's I found on the island is located here (one in the airport & one inside Golden Tulip Grande Hotel).
2. The Beaches
Comoros may be a small nation, but wow does it have some beautiful beaches. Even better that the beaches also have virtually zero tourists. You'll see some locals scattered around, but they really are very untouched. The island as a whole has a big problem with plastic, but this seems more in the forest areas with the beaches unaffected. The stand out beaches were Chomoni, Bouni, and Galawa.
3. Mount Karthala
Mouth Karthala is an active volcano and also the highest point in The Comoros at 2,361 metres. There's been over 20 eruptions since the 19th century, so it's definitely pretty active. This is a great half day adventure, but you've definitely got to be of a reasonable fitness level. There's evergreen forest up until around 1,800 metres and then the landscape changes competely. I set off at 4am and I'm glad I did, as the whole adventure took 9 hours total to go up and down. Worth noting that you can go a good 50% of the way by car if needed. The view are so worth it!
4. Boat Ride
At the private beach cove within the Golden Tulip Grande Hotel there are plenty of locals with wooden boats that they use for fishing. None of these people will approach you, but you can approach them and ask for a short boat ride (approx $5 tip) to some nearby caves that are only 200 meters away along the coastline. The boats don't have a motor, so it's a really authentic experience watching your local boat master in action.
5. Lac Salé
In the northern part of the island you'll find Lac Salé. The small crater lake is in a picturesque spot next to the coastline. This has became a sacred spot for locals as they believe the lake is bottomless. This goes back to a story some years ago where two divers went down to explore and never returned. This is a definite spot to use a wide-angle camera lens!
6. The Wildlife
There's not a huge abundance of wildlife on the island, but there's one that makes the country very unique. Maki is a type of Lemur and the only Lemur species located outside of Madagascar. You'll see them spread across the forestry of the island. Very fascinating creatures to watch and photograph. If you're struggling to locate them, let your driver know and I'm sure he'll know the spots.
There also seems to be plenty of tortoise located around the grounds of Golden Tulip Grande Comore Hotel.
7. Rock Formations
There's a number of large rock formations located along the coast of the island. You'll find virtually zero information online about these. They're likely to be volcanic due to the history of the island, but I'm no geologist. Either way, they're very unique! You'll see these rock formations as you're driving along the island. A short 15-20 minute hike will take you up to these black rocks. You'll also get a great view of the coastline.
There's not a huge selection of hotels across the island, but Golden Tulip Grande Comore Moroni Resort & Spa is the stand out highlight. As far as the island goes, it's a very nice resort. All of the rooms are ocean facing, with the option of self-contained bungalows overlooking the private beach. Service standards are good with staff always on hand. You're looking at $100 a night, so there's definitely cheaper alternatives.
I found the selection of food on the island pretty basic. Most food and drink is imported, which means there wasn't even a local beer on hand to try. There are plenty of small restaurants operating from the homes of locals across the island. You're basically eating inside their house, which is a unique experience. The fresh fish is obviously local and was delicious, as was the fried plantain.
Note: These above tips are based on Grande Comore Island.