IRS Publication 525, Taxable and Nontaxable Income (2018), page 31 - https://www.irs.gov/pub/irs-pdf/p525.pdf#page=31
Free tour. If you received a free tour from a travel agency for organizing a group of tourists, you must include its value in your income. Report the FMV of the tour on Schedule 1 (Form 1040), line 21.
Fair Market Value is what the cost of the tour would be if it was not free.
