Leer en la biblioteca es tranquilo.

to be

Breakdown of Leer en la biblioteca es tranquilo.

• en: in
• la biblioteca: the library
• tranquilo: peaceful

Questions & Answers about Leer en la biblioteca es tranquilo.

Why is leer in the infinitive form instead of something like leyendo?

In Spanish, the infinitive (here leer) can function as a noun, similar to "reading" in English.

• Leer en la biblioteca es tranquilo.
  → Reading in the library is relaxing/peaceful.

Using leyendo would be wrong here because leyendo is a gerund/participle used for continuous actions, usually with estar:

• Estoy leyendo en la biblioteca.
  → I am reading in the library.

So when you want "reading" as the subject of a sentence (a general activity), use the infinitive: leer, not leyendo.

What is the subject of the sentence?

The subject is the whole phrase leer en la biblioteca (“reading in the library”).

Grammatically:

• Leer en la biblioteca = subject
• es = verb
• tranquilo = predicate adjective describing the subject

So the structure is like:
[Reading in the library] is [relaxing/peaceful].

Why is it tranquilo (masculine) and not tranquila to agree with biblioteca?