Are your players complaining that your games are too easy? Well, then they (or you) might enjoy an adventure through the land of Chult as you run the infamous Tomb of Annihilation, known for being the hardest campaign inDungeons & Dragons, or at least the hardest in fifth edition.
Still, with high difficulty in mind, it’s important to pay close attention to the party’s level. While you’re able to throw random encounters until they level up (or die), you can also use milestones and make sure your players are at the appropriate level when reaching certain locations of the adventure. Thus, we’re here to suggest a few moments for said milestones.

There will be spoilers for the adventure.
Suggested Levels
Though the book doesn’t have a milestone guide like newer adventures, it does have a table of suggested levels for certain chapters of the campaign. It suggests you should have the party be at least level five when starting Dwellers of the Forbidden City, at least level seven when starting Fane of the Night Serpent, and at least level nine when starting Tomb of the Nine Gods.
Because of the campaign’s difficulty, we recommend taking these suggestions to heart. If the party enters an area while under-leveled, feel free to throw a ‘random’ encounter that levels them up and restores some balance (we’ll talk more about these later).

6Port Nyanzaru
You Could Reach Level Three Here
This city is interesting when it comes to leveling up your party. The main goal here is just conversation and getting ready to explore the land, so there’s nothing big here that could trigger a milestone. However,you can do a lot in a city.
Nyanzaru is filled with NPCs and extra things to do, such as racing and shopping, and the book offers you ten side-quests. you’re able to pick your favorites (or see which ones the players are interested in) and level them up. There are so many, in fact, that you can take them, split them in half, and level them up once each half is done, thus making your players level three when leaving the port.

5The Land Of Chult
Where Should We Start?
This area is one of the trickier parts when making milestones. There are a lot of places the party can go, and you don’t know which one they’ll choose or accidentally go by getting lost. Still, you can have them level up after completing each main location (if they didn’t do a lot at the port and are level one) or every two or three locations (if they’re entering this area at level three or higher).
There’s also the fact that they may skip certain places due to never finding them, so adjusting the milestones as they go is important. If they’re entering at level three, we suggest the following:

Alternatively, you can focus solely on numbers and level them up for every two or three places they complete.
4Random Encounters
Or Rather, Not-So-Random Encounters
As we mentioned, there’s a bit of uncertainty about whether your players will hit all the spots above. Unless you give them a clear indication of how to get to all the places stated, they might skip them without realizing it, or they may just not feel like going everywhere.
A solution to improvise extra milestones is through’random' encounters.Prepare a few, either from the random encounters table or by getting some of the monsters from the campaign, and have them ready to attack the party while they’re going from point A to B.

For instance, if your party reaches Omu but they’re still level four, have a big random encounter before it, let them have a long rest, saying that the city is still one day away, wrap it up as they arrive there, and level them up.
3Gather The Cubes
Welcome To Omu
Once the players reach Omu, they can pretty much stay here until the end, as the Soulmonger is here (in a tomb, but still here). However, to get to the tomb, they need to collect nine puzzle cubes, and that takes a while.
Each of them is located in a different shrine, and there are traps to get there. Not to mention, other NPCs will also be after them. Thus, getting all of them is quite the achievement, one worthy of a level-up.

Omu is big and filled with enemies who can ambush the party as they go, so if there is too much extra trouble in your story, it might be worth a second level-up. Random encounters against groups of people can also happen inside the city.
2Defeating Ras Nsi
Dealing With The Yuan-Ti
Among the many enemies the party will face,the Yuan-Tiare some of the most prominent. Their leader stays in the Fane of the Night Serpent, and the players can go there willingly, or they can be captured. Or you can use other ways to make this dungeon part of the narrative, such as having the Yuan-Ti obtain puzzle cubes before the players.
Regardless of how you incorporate this temple into the narrative, it’s essentially a good old dungeon with monsters, treasure, and a boss at the end. Thus, leveling the party up once they complete said dungeon is more than fair.

We’re offering more milestones than you need to have your players reach level 11, so pick the ones you want to use the most or use some to replace milestones your players didn’t complete, such as not doing all side-quests or skipping locations.
1Tomb Of The Nine Gods
Perfect For Adjusting Remaining Milestones
The final area in this game is also a dungeon, but it’s a big one. It has six levels (six floors), and they can challenge their brawn and brain with monsters and puzzles.
The book recommends that they be at least level nine here, and we recommend that they reach their maximum level (11) before the sixth floor so they can fight with everything they have. You can also take this opportunity to let them go above 11 if you so choose.

If they reach the tomb at level nine, you’re able to put milestones for completing floors two and four (or three and five), or you can put a single milestone after completing the third floor if they were already level ten when they arrived. If they are below nine when they arrive here, you can just add extra milestones for completing floors in whichever manner you please.
Alternatively, you can match these milestones with whatever location they are when you wrap your session; if they did a good chunk for the day, make this chunk a milestone, regardless of the floor they are on. They likely won’t need a milestone per floor, as that would be five milestones, and going through this tomb at level six would be quite a challenge.