Most likely 'search' as you already mentioned, would prove to be the most useful option here. But to make sure, you can think about this approach. Get answers

Most likely 'search' as you already mentioned, would prove to be the most useful option here. But to make sure, you can think about this approach. Get answers to these questions - (1) understand who the end users are (2) what problem are you trying to solve for them? (3) What kind of knowledge would they have before coming to this website? (4) What kind of information would they be searching on the site? Each of these questions will have multiple answers. You will have to talk to the stakeholders (business owner, marketing dept etc.) to get this information. At the end of this exercise, you should be able to make groups of your end users. Could be 3 to 7 depending upon various demographic factors (1) age (2) location (3) domain knowledge (4) expectation etc. Once you have these user groups decided, make profiles for each of the group. Profile basically describes that particular section of your user audience based on various characteristics like age, gender, education, language, computer experience, domain expertise and their expectation from the website. Then the most challenging part - talk to at least 10-15 'real' users from each of your user groups and validate the 'expectations' part that you assumed above. In addition to that you can also try 'card sorting' and 'reverse card sorting' approaches to see how your users categorize the information you have. People who are from Usability Analysis field, will understand what I'm talking about here, but @polyfractal, you can trust this as a proven scientific method for Information Architecture of your website content.