Poland's underwater hotel has world's deepest indoor dive

This Polish hotel has built the deepest pool in the world. Photo / Supplied

Poland is an unlikely destination for diving fanatics.

With roughly 400 km of frigid coastline on the Baltic Sea, you'll find no coral reefs or schools of rainbow fish here.

You will however find the world's deepest diving pool at an unassuming hotel in Mszczonow near Warsaw.

The DeepSpot diving pool is 45 metres deep and filled with 8000 cubic metres of water. It's an artificial ocean around 27 times the size of an Olympic pool.

In short it's the perfect sport for scuba enthusiasts or new learners.

The tiled walls and overhangs provide plenty of challenges to explore, and in them you'll find windows looking out from the hotel conference rooms and suites.

Even non-swimmers can enjoy the sub-aqua setting.

View this post on Instagram

Imagine having 45 meters of water above your head. In a pool! 😈 : : : #deepspot #diving #freediving #scubadiving #visitpoland #mszczonów

A post shared by Deepspot (@deepspotpoland) on Jul 5, 2018 at 10:38pm PDT

An unusual feature is the glass tunnel crossing through the middle of the pool, allowing observers to experience the depths without donning an aqualung.

The building is truly colossal. It took around 1,100 tons of steel to build.

Opening to the public this autumn, the pool and hotel will provide a novel stay for its guests.

View this post on Instagram

Our underwater playground. 🌊🌊🌊😍 What would YOU do here? : : : #deepspot #underwater #indoordiving #pool #diving #scubadiving #freediving #extreme #watersports #visitpoland #mszczonów

A post shared by Deepspot (@deepspotpoland) on Jul 11, 2018 at 2:31am PDT

If visiting the depths is not your thing the company behind DeepSpot also specialises in aerial adventures.

FlySpot runs a flight simulator for visitors and enthusiasts to get a feel for controlling a full size, 80 ton, Boeing 737 jet plane.