Secrets of Atlantis is NetEnt's take on the underwater lost city theme, released in August 2016. It runs on a 5x4 grid with 40 paylines and leans heavily on two connected mechanics: the Highlight Feature that triggers Colossal Symbol re-spins, and Nudge Wilds that always expand to cover a full reel. There are no free spins here - the entire bonus structure revolves around those Colossal re-spins and the 97.07% RTP that sits well above average.
How It Plays
The game uses five reels with four rows and 40 fixed paylines. Bets range from 0.20 to 200 per spin, giving a wide staking window. Symbols include various gems, golden ornaments, and Atlantean artefacts set against a deep ocean backdrop with art deco styling on the frame and borders. The visual presentation is polished - blues, golds, and greens with light effects filtering through the water.
Hit frequency sits at 23%, so you land a win roughly every four spins. The base game pays are steady without being spectacular, which fits the medium volatility (5.3 out of 10). Most of the heavier lifting comes from the Highlight Feature and Nudge Wilds working together.
The Highlight Feature and Colossal Symbols
This is the centrepiece of the entire game. On any spin, symbols on reels 2, 3, and 4 can randomly become highlighted - they glow with a golden border. If all visible positions on those three reels get highlighted in the same spin, you trigger a Colossal Symbol Re-Spin.
During the re-spin, reels 2, 3, and 4 merge into a single oversized reel that displays Colossal Symbols - massive 3x4 blocks that fill the entire merged area. Reels 1 and 5 spin normally while the middle section shows one giant symbol. When a high-value symbol or wild fills that merged space, the payouts across 40 paylines add up quickly.
There is also a chain mechanic: if the entire merged reel gets highlighted again during the re-spin, you earn an additional Colossal re-spin. This does not happen frequently, but when it does, you are looking at back-to-back spins with massive symbol coverage across the middle of the grid.
Nudge Wilds
The Nudge Wild is a tall wild symbol that can land partially visible on a reel - maybe only one or two positions showing. When this happens, the wild automatically nudges up or down until it covers the full reel, four positions high. You always get the complete wild reel, which means every Nudge Wild effectively becomes a stacked wild.
During Colossal re-spins, a Colossal Stacked Wild can appear on the merged reels 2-4. If it lands partially visible, the same nudge mechanic kicks in and it shifts to fill the entire 3x4 merged area. A full Colossal Wild covering 12 positions in the middle of the grid while reels 1 and 5 spin around it is the game's best-case scenario, and it is where the 1,600x maximum payout becomes reachable.
No Free Spins - and That Is Fine
Secrets of Atlantis does not have a traditional free spins bonus round. Some players find that off-putting, but the Colossal re-spins essentially serve the same purpose. They trigger directly from the base game without needing scatter symbols, and the Nudge Wilds keep the base game itself productive between Colossal triggers.
The absence of a dedicated bonus round means the game does not have long dry spells where you are waiting for three scatters to land. The Highlight Feature can activate on any spin, and Nudge Wilds appear independently of it. The result is a smoother session with less feast-or-famine swings than you get from slots that lock all their value behind a bonus trigger.
RTP and Volatility
At 97.07%, Secrets of Atlantis has one of the higher RTPs in the NetEnt catalogue. The volatility rating of 5.3 out of 10 puts it in the middle of the range - you are not going to see the wild swings of a high-vol game, but the Colossal feature can produce strong individual spins that punch above what the medium rating might suggest.
The maximum win of 1,600x your total stake comes from Colossal Wilds covering the merged reels while high-value symbols line up on reels 1 and 5. It is not a jackpot-chasing slot, but for a game with this RTP and hit frequency, the payout ceiling is reasonable.
The 40-payline structure with medium volatility and high RTP makes this a solid session game. The Colossal mechanic gives you something to watch for on every spin without making the base game feel like dead time between features. If you prefer your bonus mechanics woven into the main game rather than locked behind a separate trigger, this is one of the better examples in NetEnt's library.
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