That's the adjective he used to describe the stretch Boston is set to embark on Thursday that features four games in four cities over five nights and includes a trio of the league's top teams in the Orlando Magic, Atlanta Hawks and Los Angeles Lakers.
Most coaches would dub it "grueling" or "ridiculous" -- and Rivers probably wouldn't disagree with those assessments -- but as Boston prepares to navigate this midseason obstacle course, Rivers rushes toward it with excitement.
"It's a fun stretch, one of the stretches of the season that I've been really looking forward to," said Rivers. "It's good for us. We're coming off injuries and we're probably in a bit of disarray because of that, so there's really nothing better than really getting tested by great teams. That will teach you a little something about your team."
As recently as last week, this sort of schedule was the last thing the Celtics needed. Boston limped through an injury-plagued stretch that saw the team drop eight of 12 before Kevin Garnett returned from a hyperextended right knee to provide a much-needed spark after a 10-game absence.
With Garnett, the Celtics have put together back-to-back wins for the first time since the start of the month, but they haven't exactly looked like world-beaters in doing so. Now they must face three teams with world championship aspirations.
Fortunately for Boston, this might be exactly the motivation it needs.
As Rivers is fond of noting, sometimes his team is its own biggest enemy as it struggles to focus on regular-season games when the ultimate goal lies further ahead.
Matchups against other teams among the NBA elite will require no such search for inspiration.
"These are big games -- big, big, big games," said Celtics forward Glen Davis. "If you're not a competitor, you don't need to play in these games. It's a great opportunity for us to keep our winning streak alive and also get better against playoff-contending teams. We're looking forward to the challenge, every game should make us even better."
Rivers wouldn't mind if the games had been spaced out a little more. He joked "go ask TV," when talking about a schedule that features a national broadcast Thursday in Orlando, and another when the Lakers visit TD Garden Sunday.
Regardless of the difficulties inherent with the schedule, Paul Pierce is setting the bar high as the Celtics approach full health. Forward Brian Scalabrine is expected to be available beginning Thursday, leaving guard Marquis Daniels as the only significant missing piece.
"We set a goal of winning every game before the All-Star break," said Pierce. "It'll be nice to get everybody back into it. We've played pretty much the whole season without a healthy [roster]. We'll get everybody back and get rolling. It's a long NBA season."
Rivers admits this stretch won't be defined by wins and losses, and doesn't envision it as any sort of significant measuring stick.
"You want to win them and they're special games because they're against good teams, which makes it a lot of fun," said Rivers. "Having said that, you can't use it as a measuring stick, at least I can't, because you don't know what those other teams are going through. The Lakers might be on a long road trip, or Orlando could be playing well -- or not playing well -- and same with Atlanta.
"In the playoffs, you're getting the best of that opponent," Rivers said, adding that this stretch is a measuring stick "for this moment, maybe this month, but it won't matter when you get to the playoffs."
These three games could impact the playoff seedings as the Celtics (29-13) have both the Magic (29-16) and Hawks (29-15) breathing down their necks in the Eastern Conference standings. Even so, it likely will be hard to remember these games once summer rolls around.
"Once we get to late April, this will have been great entertainment, but then you're down to the business of what we are here for," said Ray Allen. "Right now, we're just jockeying for position [in the playoffs] and hopefully we get a good position."
Ultimately, the Celtics say they are approaching this stretch with the same goal they have for every game: improve over the last performance.
While Monday's victory over the Clippers wasn't the prettiest win, Rivers said he thought it was a step forward. Riding this mini two-game winning streak, the Celtics will look to continue that upward trend.
"We're improving, I told our guys that's what I enjoyed about [the Clippers game] -- that we were a better team when that game was over," said Rivers. "That's all I look at. The whole momentum thing, I don't look at that. I'm looking at if we're improving, or did we stand still. Win or lose, as long as we didn't take a step backwards. [Monday's] game was a step forward -- movement-wise, intensity on defense -- that's what we've got to keep doing. Our job is to get better each game until the playoffs."
After all, the fun doesn't really start until the postseason.
Chris Forsberg is a roving reporter for ESPNBoston.com. Follow him on Twitter.