Saturday's Champions League final between Cristian Ronaldo's Real Madrid and Gianluigi Buffon's Juventus will take place amid taut security following last week's terror attack in Manchester.
The suicide attack at Manchester Arena, which left 22 dead and 116 injured, means vigilance will be heightened, but unprecedented security measures were already in place for the game.
"The security operation for the four-day period covering June 1-4 will be the biggest ever seen for a sporting event in the UK," says the Football Association of Wales (FAW).
Most noticeably, the retractable roof of the Principality Stadium will be closed, making it the first Champions League final to be played in indoor conditions.
The FAW said security was the "primary factor" in the decision to close the roof, although there is no evidence of a security threat against the final.
Fans will not be allowed to bring bags into the stadium, which will have a reduced capacity of 66,000 for the match, and have been encouraged to use left-luggage facilities in the city centre.
They have been urged to arrive no later than two hours before kick-off to allow time for security checks.
The city of Cardiff has also launched a smartphone app, 'EVAC Cardiff', which alerts people to major incidents such as acts of terrorism.
It will also provide information, such as directing people to their nearest evacuation point.
Around 1,500 police officers are due to be on duty in the Welsh capital over the weekend, with local units supported by specialist officers from other areas of the United Kingdom.
As the Principality Stadium sits slap-bang in the middle of Cardiff, there will be road closures in place around the city centre on the day of the game.
There will also be tight security around the four-day 'UEFA Champions Festival', which takes place on the picturesque seafront at Cardiff Bay and is expected to attract over 200,000 people.
Events include a match between retired greats on Friday, due to take place on a floating pitch, and a DJ set by former Valencia and Barcelona midfielder Gaizka Mendieta on Saturday.
- Threat level downgraded -
Restrictions have been placed on water travel in the Cardiff Bay area and on Cardiff's River Taff, which streams right past the stadium.
"This will be the biggest security operation undertaken in the city since the (2014) NATO summit," South Wales Police assistant chief constable Richard Lewis told AFP.
"The security team has liaised with all concerned partners in relation to these measures, which are deemed an appropriate action in the circumstances."
European governing body UEFA says fan zones will remain open under "strict security measures".
But as for previous finals, the match will not be shown live on big screens in fan-designated areas.
Congestion due to road closures led to Lyon's women's team arriving late for their pre-match training session on Wednesday ahead of Thursday's Champions League final against Paris Saint-Germain.
"Would a delay like that have been allowed to happen with the boys? I don't think so," complained Lyon coach Gerard Precheur, whose side take on PSG at the Cardiff City Stadium.
Madrid talisman Ronaldo cancelled a sponsor event in London last Saturday after the UK's terror threat level was temporary upgraded to "critical", meaning an attack may have been imminent.
The threat level has since been downgraded to "severe".
"These days, we all have security concerns, all the time," said UEFA president Alexander Ceferin on Thursday.
"Time changes, but there is very good co-operation with the local authorities and the London authorities.
"The event today (the women's Champions League final) and the event on Saturday will be safe." afp