労働者たちはくつろげる酒場に集まることが好きである。

。

The workers liked to gather at a comfortable bar.

Literal

Workers [topic-は] relax-can bar [to-に] gather [nominalizer-こと] [subject-が] liked.

くつろげる ('can relax') is the potential form of くつろぐ, used as a relative clause modifying 酒場. 集まることが好き uses こと to nominalize the action. A humanizing detail about workers' social lives.