Football theatre in one of its great cathedrals
The outcome might have been a stalemate, but there was nothing stale about the atmosphere at the Vicente Calderon on an memorable European evening.
It is still almost three hours until kick-off when my taxi is ushered to pull over by armed police. We are two blocks from Estadio Vicent Calderon and the roads are closed down, restricted to authorised vehicles only.
I'll be walking the rest of the way.
Dozens of merchandise carts line the open avenues between us and the formidable wall of the stadium - the most imposing of football fortresses by the river by which it was once named - the Manzanares.
Food vendors scatter the streets peddling everything from pumpkin seeds to hotdogs, drinks and confectionary. Atletico Madrid fans are spilling out of bars and chewing seeds on the street corners. The ground is littered with husks. Riot police gather in clumps around the eastern side of the ground - there to strategically manage the arrival of the opposing fans.
Despite Atleti having four away goals in its locker, this doesn't feel like the victory lap I'd been expecting. The fans seem edgy in their excitement, tempered in their anticipation. Across town the Bayer supporters had been gathering in their hundreds at Madrid's picturesque Plaza Santa Ana, their drum beats and chants echoing across the balmy afternoon air.
Atleti may not have lost in its last 20 matches at the Calderon, but this one feels far from over.
As kick-off draws nearer, the fans swell. The outside of the ground feels like a street party, with no-one in a Bayer Leverkusen shirt invited.
The police numbers grow too, at one point six armoured vans snake through the throng.
Finally, the Bayer fans turn up, a little late to the show, but in fine spirits. The first wave are ushered in via the North-Eastern corner, as mounted police clear a path through the Alteti supporters to the gates.
The rest are brought in on the south-western side in groups of around 50. They seem outnumbered by about 20-1, but they are in full voice, hurling abuse at the Atleti team bus as it rolls past, cheering the Bayer bus and greeting the rest of us with the universal one-fingered salute. Guards at the gate issue thorough searches and one fan triumphantly removes his cap to show there are no weapons hidden underneath it.
While the anxiety among the hordes of home fans is palpable, the travelling comparative few from Bayer enter the stadium with a plucky swagger.
What started in the plaza and on the streets hours earlier builds to a crescendo within the ground as the UEFA Champions League anthem reverberates around the packed crowd. I've sat through countless renditions of the tune watching matches on television. Live it bursts to life, the fans thundering applause as the last strains of English composer Tony Britten's anthem play out.
This is spine-tingling stuff.
To the match and Bayer holds its own, dominating possession if appearing bereft of ideas in the Atleti box. Atletico 'keeper Jan Oblack, fuelled by the occasion and perhaps with half a mind on what happened to PSG in neighbouring Barcelona last week, plays like a goal-keeper possessed, providing one of the great triple-saves to keep his side in control of the tie, if not the match.
Star French forward Antoine Griezmann is a constant threat on the counter-attack, the crowd rising and falling with his every touch. Spain midfielder Koke is everywhere. Marshalling his Atleti team-mates, mucking in in defence, and providing the creative outlet for its attack.
Atleti manager Diego Simeone is the most animated man in the room, writhing, dancing, twisting, agitating, as his team goes close to securing the win, but ultimately has to settle for the draw. Atleti's hard work in the first leg has paid off. Oblack has produced a mighty individual performance befitting the sporting cathedral which has hosted it.
We all leave feeling drained but satisfied. The score says it was stalemate, but the heroic individual performances and the theatre of opposing fans desperate to see their team win, set against the backdrop of one of football's great modern cathedrals, has made this a most memorable European evening.
