Advanced map

Sunken Columns

Info

Sunken Columns is an Advanced map added in update 30.0 (February 2022). It is a tribute to the Basalt Columns map from Bloons TD Battles 2, set in a rocky cavern of hexagonal basalt columns.

Layout and path. Two lanes run at the same time and cross over each other:

One lane enters at the top middle-left, swings over to the top right and exits at the bottom middle-left.
The other enters at the top middle-right, swings over to the top left and exits at the bottom middle-right.

So each lane travels to the opposite side of the map and back. The lanes overlap and intersect in big bends at the top and bottom of the map, and these intersections are the heart of every strategy. Near the top, bloons from both entrances pass very close to each other, which makes it a great spot for spawn camping.

The sunken columns. Two large basalt depressions in the middle sit far below the rest of the map. Towers placed down there can barely see the track: only four narrow river strips give them a view. Even a Carrier Flagship deck does not lift towers high enough, although a 0-0-4 or 0-0-5 Dartling Gunner on a Flagship deck can shoot over. Use the depressions for towers that ignore line of sight, global-range towers or support towers.

Ponds. Each depression contains a pond for water towers. Either pond can be drained for $1,000 ($2,000 for both) when no water towers are on it, turning it into land.

Space. The bottom-left and bottom-right corners are wide enough for two Banana Farms each.

Water: yes. Line of sight: blocked by the depressions. High ground: none of note.

Sunken Columns is slightly easier than an average Advanced map because the overlapping bends give limited-range towers huge value.

How to beat Sunken Columns

Map overview for strategy

Sunken Columns rewards one simple idea: build at the intersections. The two lanes overlap at the big bends at the top and bottom of the map, so towers placed there hit bloons from both lanes, often more than once.

What to know:

The top column area where bloons from both entrances come together is the best spawn-camping spot. High-damage towers packed there handle most rounds.
The depressions are a trap for normal towers. Anything placed in the sunken middle sees only through the narrow river strips. Keep them for farms, Villages that buff towers on the rim, global towers like Monkey Aces, or Dartling BADS turrets.
Draining a pond for $1,000 gives extra land, but only if you are not using it for water towers.
Stall the overlaps. The overlapping sections are short, so stuns and glue keep bloons where your damage is.

Best towers

Boomerang Monkey 5-2-0 (Glaive Lord): placed near an intersection, its orbiting glaives wipe out super ceramics and low-tier blimps, and its ricocheting glaives bounce between the separated lanes for massive damage.
Glue Gunner 0-2-5 (Super Glue): its splats lock large groups of bloons and blimps in place on the short overlap sections. Excellent with Sauda.
Glue Gunner 5-x-x (The Bloon Solver), Tack Shooter 2-0-5 (The Tack Zone), Ice Monkey 5-x-x (Super Brittle): all strong at the top intersection where bloons merge.
Monkey Village 3-2-0 (Primary Training) and two Alchemists: the classic support package for a top-intersection kill zone.
Monkey Ace: global range from the depressions.
Dartling Gunner 0-0-4 or 0-0-5 (BADS or Bloon Exclusion Zone): placed on a Carrier Flagship deck in a pond, it can fire out of the depressions.

Best heroes

Sauda: the best fit. The overlapping bends boost her main attack, and her Sword Charge hits bloons in the overlap multiple times. With Relentless or Super Glue stuns, she deals huge damage to bloons and blimps.
Obyn or Geraldo: solid support alternatives at the top intersection.
Admiral Brickell: if you want to use the ponds for water towers.

Easy and Medium

Put your hero and a Dart Monkey at the top intersection, add a Tack Shooter and Boomerang Monkey there too. Get camo by round 24, and a 0-3-2 MOAB Mauler or Glaive Ricochet for round 40. Finish with Glaive Lord or Tack Zone.

Hard

Sauda at the top intersection, Tack 2-0-4, Village 2-2-0, Alchemist 3-0-1 and Relentless Glue. Add Glaive Lord and Super Glue for the late game.

CHIMPS

A Sauda-centred CHIMPS route at the top intersection:

Round 1: Sauda at the top bend where both lanes overlap, plus a Dart Monkey.
Rounds 2 to 15: Tack Shooter next to her, upgraded towards 0-0-3. A Boomerang going 2-0-0 if needed.
Rounds 16 to 30: Village 0-2-0 by round 24 for camo, then 2-2-0. Tack to 2-0-4 Overdrive.
Rounds 31 to 50: Glue Gunner towards 0-2-4 Relentless Glue, Alchemist 3-0-1 on the Tack. Boomerang towards 3-2-0 Glaive Ricochet. Round 40 is handled by Overdrive and Sauda.
Rounds 51 to 70: Boomerang to 4-2-0 MOAR Glaives, Ice Monkey 4-0-1 Embrittlement, second Alchemist.
Rounds 71 to 90: Boomerang to 5-2-0 Glaive Lord, Glue to 0-2-5 Super Glue.
Rounds 90 to 100: DDTs are covered by Embrittlement and Village camo. For round 100, Super Glue stuns the BAD while Sauda and Glaive Lord burn it down. Optionally upgrade the Tack to Tack Zone.

Impoppable

Same top-intersection plan. Get Super Glue a little earlier and consider a Perma-Spike on the rim near the exits as insurance.

Other modes

In Half Cash, the top intersection is even more important: put every early dollar there and skip pond draining. On Apopalypse, rounds come back to back with no breaks, so build Relentless Glue early to stop dense waves from flooding the short overlap sections. In Alternate Bloons Rounds, blimps appear earlier, so get Glaive Ricochet and a MOAB answer at the top intersection sooner than usual.

Dangerous rounds on this map

Round 24: first camo.
Round 40: first MOAB; blimps spread across both lanes after the top intersection.
Round 63: a ceramic rush through the overlap.
Rounds 90 to 100: DDTs and the BAD; stuns are key.

The BTD6 Master YouTube channel has video guides for Sunken Columns if you want to see the intersection build in action.

Frequently asked questions

What is Sunken Columns based on?

It is based on the Basalt Columns map from Bloons TD Battles 2 and was added in update 30.0.

Can towers in the sunken columns hit bloons?

Barely. Line of sight is blocked except through four narrow river strips, so use the depressions for global, support or line-of-sight-ignoring towers.