Noun which may take the genitive case particle 'no', Taru adjective, Adverb taking the 'to' particle
very interesting; of absorbing interest; having a keen interest (in); being immensely curious (about)
Yojijukugo (four character compound)
この本は興味津々たるものがあって飽きない。This book is so absorbing that I can't put it down.
Also written 興味しんしん【きょうみしんしん】、興味津津【きょうみしんしん】