The Hollow Floor 3 Puzzle: how to solve the Grave Lock

The Hollow Floor 3 puzzle at a glance

The rule behind The Hollow Floor 3 puzzle is arithmetic, not wordplay. Every gravestone shows a symbol, a name and two dates. Subtract the birth year from the death year for all eight, pick the three smallest results and enter their symbols from the shortest life to the third shortest.

Step 1: find the graveyard room on Floor 3

Ride the elevator in The Hollow hub and choose Floor 3. The maze is themed on Demonology, and the Biter roams the corridors, so move carefully and stop when you hear it nearby.

The maze layout changes each time you enter, which means the room for The Hollow Floor 3 puzzle does not have a fixed location. Players have found it on the left side of the map more than once, including near a theatre-like room and in a room with four posters on the wall, but you should treat those as hints rather than a route. You will know you are in the right place when you see a coffin in the middle of the room surrounded by gravestones.

Step 2: read the poem and the gravestones

From the entrance, walk forward and look to your right for a large sheet of paper with a poem on it. The poem is the hint for The Hollow Floor 3 puzzle: it tells you the lock wants the three people who died youngest, in order.

Then walk up to each gravestone. Each one shows a person's name, a symbol and their birth and death dates. The symbols seen so far are the Broom, Ghost, Witch's Hat, Bat, Spider, Cauldron, Pumpkin and Scared Cat. Write down or screenshot the symbol and both years for every stone.

Step 3: work out the three shortest lives

For each of the eight gravestones, subtract the birth year from the death year. That number is how long the person lived. Sort the eight results from smallest to largest and keep the first three.

Here is a worked example of The Hollow Floor 3 puzzle using numbers one player reported. Your gravestones will probably show different dates, so do the maths with your own:

In that run the answer was Scared Cat → Ghost → Spider. Do not copy it blindly: the dates, and sometimes the symbols attached to each date, can change between players and runs. The calculator on this page does the subtraction and sorting for you.

How to use the Grave Lock calculator

The calculator at the top of this page does the maths for you. For each gravestone, choose its symbol from the list and type the birth year and the death year. As you fill in rows, the calculator shows each person's age and highlights the three shortest lives in green. The answer box then shows the exact order to set on the Grave Lock: slot I, slot II and slot III.

If two people lived the same number of years, the calculator warns you. In that case look again at the full dates on those two gravestones and enter them as year-month-day, so it can tell who lived a few months less. Everything stays in your browser, so you can clear it and start again on a new run of The Hollow Floor 3 puzzle as often as you like.

Step 4: enter the code on the Grave Lock

1. Walk up to the coffin in the centre of the room to open the Grave Lock.
2. Press M to unlock your mouse cursor if you are on a computer.
3. Click the buttons on slot I until it shows the symbol of the person with the shortest life.
4. Set slot II to the second shortest life and slot III to the third.
5. Press Open. If the order is right, the coffin opens and you can take the Third Night Relic.

The order matters. Starting from the left, the shortest life always goes first. Entering the right three symbols in the wrong order is the most common reason The Hollow Floor 3 puzzle seems not to work.

Step 5: escape with the relic and claim Festering Felix

With the Third Night Relic in hand, head back through the maze to the elevator. The Biter is still around, so retrace your route rather than exploring new corridors. Take the elevator up to the hub, and the Festering Felix badge and the free Festering Felix head accessory unlock. You do not need any Robux to get it.

Why your Grave Lock code is not working

If the coffin will not open, one of these is almost always the reason:

• You only read three gravestones. All eight count, and they are spread over several rooms.
• A subtraction slipped. Double-check each age, especially when birth years cross into a new century.
• You sorted by birth year. The order is by how long people lived, not by when they were born.
• The order is reversed. Shortest life goes in slot I, starting from the left.
• You copied another player's answer. Answers can differ between players and runs. Use your own gravestones.

If two people lived the same number of years, look at the full dates on those gravestones to see who lived a few months less. The calculator flags ties for you.

The Demonology quest on night three

The Hollow Floor 3 puzzle is not the only reward on night three. The Demonology partner quest sends you into a black-and-white realm to collect six relics — the Altar Lantern, Stygian Hourglass, Grimoire, Devil Mirror, Cursed Lock and Skull of the Allseer — and place them on the altar. Leave through the glowing door to earn the Way Back badge and the Biter Fedora head accessory.

See every floor, quest and reward in our Roblox The Hollow guide, or go back to the Floor 2 puzzle if you skipped it.