“Que” is a relative pronoun here. It has for grammatical function that of “attribut du sujet”, the subject being “le Grand Canyon” (Le Grand Canyon est “qu'” (“désastre écologique” is the antecedent)); there is a subject/verb inversion in the clause and as well an unusual place for the “attribut”. You’ll find this at the TLFi’s entry « que », (II.B.2.a).

2. [Que a pour fonction]
   a) [attribut] L’homme qu’il est. Le vieillard que je suis devenu a peine à se représenter le furieux malade que j’étais naguère (MAURIAC, Nœud vip., 1932, p. 14).

The literal translation of this turn seems to be rare in modern English or to not exist; I do not remember it. The comment by user Destal as to the incertitude of finding this form in modern English shows that it could be rare or obsolete or never have been part of the language. The following syntax is equivalent though.

• Why do you admire so much such an ecological disaster as The Grand Canyon?