The superlatives of the adjectives in Spanish can be done in two ways; the first is to put the adverb "muy" before the adjective, and the second is to add the suffix (ísimo).
In some adjectives it is necessary to change the terminations to form the superlative.
In the case of the adjective "bajo" is an example of the latter since the last letter "o" must be changed to the "i" and that is the word "bajísimo". It is also a word esdrujula for its accentuation and has tilde in the first letter "i".
