Complex sentence: Surrounded on three sides by Lough Ree and one side by Athlone town itself, its population has grown since the Celtic Tiger from around 400 in the 1990s to roughly 5000 in the early 21st century.
Split into simpler sentences: Surrounded on three sides by Lough Ree and one side by Athlone town itself. Its population has grown since the Celtic Tiger from around 400 in the 1990s to roughly 5000 in the early 21st century.